Revert "Run iOS tests on multiple shards."

This reverts commit 5a71f1585875a9ef80b79d9f247d1e21319a17d6.

Reason for revert: Turns out all the tests are running on all the shards.

Original change's description:
> Run iOS tests on multiple shards.
>
> Bug: b/230824012
> Change-Id: I6d27a8ed2c07eb76972b3bbe3679f6346ba58e06
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261306
> Reviewed-by: Christoffer Jansson <jansson@webrtc.org>
> Commit-Queue: Jeremy Leconte <jleconte@google.com>
> Cr-Commit-Position: refs/heads/main@{#36796}

Bug: b/230824012
Change-Id: Id353501f07156ccc109abf94e6d2a22014a5e767
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261562
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Christoffer Jansson <jansson@webrtc.org>
Commit-Queue: Jeremy Leconte <jleconte@google.com>
Cr-Commit-Position: refs/heads/main@{#36807}
diff --git a/infra/specs/client.webrtc.json b/infra/specs/client.webrtc.json
index 166c9da..574b9cb 100644
--- a/infra/specs/client.webrtc.json
+++ b/infra/specs/client.webrtc.json
@@ -9211,8 +9211,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 2
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -9261,8 +9260,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -9458,8 +9456,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -9804,8 +9801,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 4
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },
@@ -10202,8 +10198,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 2
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -10252,8 +10247,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -10449,8 +10443,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -10795,8 +10788,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 4
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },
@@ -11193,8 +11185,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 2
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -11243,8 +11234,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -11440,8 +11430,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -11786,8 +11775,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 4
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },
diff --git a/infra/specs/internal.client.webrtc.json b/infra/specs/internal.client.webrtc.json
index a4e8d9a..7ef9550 100644
--- a/infra/specs/internal.client.webrtc.json
+++ b/infra/specs/internal.client.webrtc.json
@@ -134,8 +134,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 2
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -179,8 +178,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -488,8 +486,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 4
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       }
@@ -684,8 +681,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 2
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -729,8 +725,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -1038,8 +1033,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 4
+          "service_account": "chrome-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       }
diff --git a/infra/specs/mixins.pyl b/infra/specs/mixins.pyl
index 1a379ac..df8ce7b 100644
--- a/infra/specs/mixins.pyl
+++ b/infra/specs/mixins.pyl
@@ -261,21 +261,6 @@
       }
     }
   },
-  'shards-2': {
-    'swarming': {
-      'shards': 2
-    }
-  },
-  'shards-4': {
-    'swarming': {
-      'shards': 4
-    }
-  },
-  'shards-6': {
-    'swarming': {
-      'shards': 6
-    }
-  },
   'timeout-2h': {
     'swarming': {
       'hard_timeout': 7200,
diff --git a/infra/specs/mixins_webrtc.pyl b/infra/specs/mixins_webrtc.pyl
index 1655de0..d7a644b 100644
--- a/infra/specs/mixins_webrtc.pyl
+++ b/infra/specs/mixins_webrtc.pyl
@@ -204,21 +204,6 @@
       'result_format': 'json'
     }
   },
-  'shards-2': {
-    'swarming': {
-      'shards': 2,
-    },
-  },
-  'shards-4': {
-    'swarming': {
-      'shards': 4,
-    },
-  },
-  'shards-6': {
-    'swarming': {
-      'shards': 6,
-    },
-  },
   'shamu': {
     'swarming': {
       'dimensions': {
diff --git a/infra/specs/test_suites.pyl b/infra/specs/test_suites.pyl
index 386d5ce..92de58d 100644
--- a/infra/specs/test_suites.pyl
+++ b/infra/specs/test_suites.pyl
@@ -35,26 +35,36 @@
       'common_video_unittests': {},
       'dcsctp_unittests': {},
       'modules_tests': {
-        'mixins': ['shards-2'],
+        'swarming': {
+          'shards': 2
+        },
       },
       'modules_unittests': {
-        'mixins': ['shards-6'],
+        'swarming': {
+          'shards': 6
+        },
       },
       'peerconnection_unittests': {
-        'mixins': ['shards-4'],
+        'swarming': {
+          'shards': 4
+        },
       },
       'rtc_media_unittests': {},
       'rtc_pc_unittests': {},
       'rtc_stats_unittests': {},
       'rtc_unittests': {
-        'mixins': ['shards-6'],
+        'swarming': {
+          'shards': 6
+        },
       },
       'slow_peer_connection_unittests': {},
       'system_wrappers_unittests': {},
       'test_support_unittests': {},
       'tools_unittests': {},
       'video_engine_tests': {
-        'mixins': ['shards-4'],
+        'swarming': {
+          'shards': 4
+        },
       },
       'voip_unittests': {},
       'webrtc_nonparallel_tests': {},
@@ -86,26 +96,36 @@
         'args': ['--quick']
       },
       'modules_tests': {
-        'mixins': ['shards-2'],
+        'swarming': {
+          'shards': 2
+        },
       },
       'modules_unittests': {
-        'mixins': ['shards-6'],
+        'swarming': {
+          'shards': 6
+        },
       },
       'peerconnection_unittests': {
-        'mixins': ['shards-4'],
+        'swarming': {
+          'shards': 4
+        },
       },
       'rtc_media_unittests': {},
       'rtc_pc_unittests': {},
       'rtc_stats_unittests': {},
       'rtc_unittests': {
-        'mixins': ['shards-6'],
+        'swarming': {
+          'shards': 6
+        },
       },
       'slow_peer_connection_unittests': {},
       'system_wrappers_unittests': {},
       'test_support_unittests': {},
       'tools_unittests': {},
       'video_engine_tests': {
-        'mixins': ['shards-4'],
+        'swarming': {
+          'shards': 4
+        },
       },
       'voip_unittests': {},
       'webrtc_nonparallel_tests': {},
@@ -116,15 +136,13 @@
       'common_audio_unittests': {},
       'common_video_unittests': {},
       'modules_tests': {
-        'mixins': ['shards-2', 'timeout-2h'],
+        'mixins': ['timeout-2h'],
         'args': [
           # Some tests exceed the default 180 seconds readline timeout.
           '--readline-timeout=1200',
         ]
       },
-      'modules_unittests': {
-        'mixins': ['shards-6'],
-      },
+      'modules_unittests': {},
       'rtc_pc_unittests': {},
       'rtc_stats_unittests': {},
       # TODO(bugs.webrtc.org/11362): Real XCTests fail to start on devices.
@@ -134,9 +152,7 @@
       'test_support_unittests': {},
       'tools_unittests': {},
       'video_capture_tests': {},
-      'video_engine_tests': {
-        'mixins': ['shards-4'],
-      },
+      'video_engine_tests': {},
     },
     'ios_perf_tests': {
       'webrtc_perf_tests': {
@@ -152,18 +168,12 @@
       'common_audio_unittests': {},
       'common_video_unittests': {},
       'dcsctp_unittests': {},
-      'modules_tests': {
-        'mixins': ['shards-2'],
-      },
-      'modules_unittests': {
-        'mixins': ['shards-6'],
-      },
+      'modules_tests': {},
+      'modules_unittests': {},
       'rtc_media_unittests': {},
       'rtc_pc_unittests': {},
       'rtc_stats_unittests': {},
-      'rtc_unittests': {
-        'mixins': ['shards-6'],
-      },
+      'rtc_unittests': {},
       'sdk_framework_unittests': {
         'mixins': ['xcode_parallelization']
       },
@@ -174,9 +184,7 @@
       'test_support_unittests': {},
       'tools_unittests': {},
       'video_capture_tests': {},
-      'video_engine_tests': {
-        'mixins': ['shards-4'],
-      },
+      'video_engine_tests': {},
       'voip_unittests': {},
       'webrtc_nonparallel_tests': {},
     },
diff --git a/infra/specs/tryserver.webrtc.json b/infra/specs/tryserver.webrtc.json
index 6bbc593..7add802 100644
--- a/infra/specs/tryserver.webrtc.json
+++ b/infra/specs/tryserver.webrtc.json
@@ -2999,8 +2999,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 2
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -3049,8 +3048,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -3246,8 +3244,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -3592,8 +3589,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 4
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },
@@ -3990,8 +3986,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 2
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -4040,8 +4035,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -4237,8 +4231,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -4583,8 +4576,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 4
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },
@@ -4981,8 +4973,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 2
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_tests/"
       },
@@ -5031,8 +5022,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://modules:modules_unittests/"
       },
@@ -5228,8 +5218,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 6
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:rtc_unittests/"
       },
@@ -5574,8 +5563,7 @@
               "path": "Xcode.app"
             }
           ],
-          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 4
+          "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test_id_prefix": "ninja://:video_engine_tests/"
       },