Revert "Add mock_rtc_event_log.h."

This reverts commit 63aea46a6e424c35f7df1ec6e702c5eeb704996a.

Reason for revert: 
Breaks Chromium build:
https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.webrtc.fyi%2Fios-simulator%2F6721%2F%2B%2Frecipes%2Fsteps%2Fgenerate_build_files__mb_%2F0%2Fstdout

ERROR at //third_party/webrtc/logging/BUILD.gn:295:5: Can't load input file.
    "../../test:test_support",
    ^------------------------
Unable to load:
  /b/build/slave/mac64/build/src/third_party/test/BUILD.gn
I also checked in the secondary tree for:
  /b/build/slave/mac64/build/src/build/secondary/third_party/test/BUILD.gn

Maybe this should be guarded by an "if (!build_with_chromium)"?

Original change's description:
> Add mock_rtc_event_log.h.
> 
> Bug: webrtc:7642
> Change-Id: Id3aa84d79e5e1a0520a968117cee550c9dd33c16
> Reviewed-on: https://webrtc-review.googlesource.com/37040
> Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#21475}

TBR=phoglund@webrtc.org,mbonadei@webrtc.org

Change-Id: Ib49c7812261c46226ec0b7b3c99af2c3a8b78add
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:7642
Reviewed-on: https://webrtc-review.googlesource.com/36981
Reviewed-by: Edward Lemur <ehmaldonado@webrtc.org>
Commit-Queue: Edward Lemur <ehmaldonado@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21477}
diff --git a/audio/BUILD.gn b/audio/BUILD.gn
index 0fd0ac8..c6de08f 100644
--- a/audio/BUILD.gn
+++ b/audio/BUILD.gn
@@ -105,7 +105,6 @@
       "../call:mock_rtp_interfaces",
       "../call:rtp_interfaces",
       "../call:rtp_receiver",
-      "../logging:mocks",
       "../modules/audio_device:mock_audio_device",
       "../modules/audio_mixer:audio_mixer_impl",
       "../modules/audio_processing:audio_processing_statistics",
diff --git a/logging/BUILD.gn b/logging/BUILD.gn
index 7c74a43..5bf99da 100644
--- a/logging/BUILD.gn
+++ b/logging/BUILD.gn
@@ -235,7 +235,6 @@
       }
     }
   }
-
   if (rtc_include_tests) {
     rtc_executable("rtc_event_log2text") {
       testonly = true
@@ -284,14 +283,3 @@
     }
   }
 }
-
-rtc_source_set("mocks") {
-  testonly = true
-  sources = [
-    "rtc_event_log/mock/mock_rtc_event_log.h",
-  ]
-  deps = [
-    ":rtc_event_log_api",
-    "../../test:test_support",
-  ]
-}
diff --git a/modules/audio_coding/BUILD.gn b/modules/audio_coding/BUILD.gn
index 53043d9..7012dff 100644
--- a/modules/audio_coding/BUILD.gn
+++ b/modules/audio_coding/BUILD.gn
@@ -2150,7 +2150,6 @@
       "../../api/audio_codecs/opus:audio_encoder_opus",
       "../../common_audio",
       "../../common_audio:mock_common_audio",
-      "../../logging:mocks",
       "../../logging:rtc_event_log_api",
       "../../rtc_base:checks",
       "../../rtc_base:protobuf_utils",
diff --git a/modules/bitrate_controller/BUILD.gn b/modules/bitrate_controller/BUILD.gn
index f50341d..267211e 100644
--- a/modules/bitrate_controller/BUILD.gn
+++ b/modules/bitrate_controller/BUILD.gn
@@ -64,7 +64,6 @@
     ]
     deps = [
       ":bitrate_controller",
-      "../../logging:mocks",
       "../../logging:rtc_event_log_api",
       "../../test:field_trial",
       "../../test:test_support",
diff --git a/modules/congestion_controller/BUILD.gn b/modules/congestion_controller/BUILD.gn
index d3e2b0e..df6599f 100644
--- a/modules/congestion_controller/BUILD.gn
+++ b/modules/congestion_controller/BUILD.gn
@@ -90,7 +90,6 @@
     deps = [
       ":congestion_controller",
       ":mock_congestion_controller",
-      "../../logging:mocks",
       "../../rtc_base:checks",
       "../../rtc_base:rtc_base",
       "../../rtc_base:rtc_base_approved",
diff --git a/modules/remote_bitrate_estimator/BUILD.gn b/modules/remote_bitrate_estimator/BUILD.gn
index ef7ee11..a5dd014 100644
--- a/modules/remote_bitrate_estimator/BUILD.gn
+++ b/modules/remote_bitrate_estimator/BUILD.gn
@@ -143,7 +143,6 @@
       "../..:webrtc_common",
       "../../:typedefs",
       "../../api:optional",
-      "../../logging:mocks",
       "../../rtc_base:checks",
       "../../rtc_base:gtest_prod",
       "../../rtc_base:rtc_base",
diff --git a/modules/rtp_rtcp/BUILD.gn b/modules/rtp_rtcp/BUILD.gn
index f07ff1ad..efa36a1 100644
--- a/modules/rtp_rtcp/BUILD.gn
+++ b/modules/rtp_rtcp/BUILD.gn
@@ -412,7 +412,6 @@
       "../../api:video_frame_api",
       "../../call:rtp_receiver",
       "../../common_video:common_video",
-      "../../logging:mocks",
       "../../logging:rtc_event_log_api",
       "../../rtc_base:checks",
       "../../rtc_base:rate_limiter",