GN Templates: Move common_config to the template.

Remove common_config from the targets' config and add
it to the template instead.

BUG=webrtc:6187
NOTRY=True

Review-Url: https://codereview.webrtc.org/2300413002
Cr-Commit-Position: refs/heads/master@{#14063}
diff --git a/webrtc/media/BUILD.gn b/webrtc/media/BUILD.gn
index 1a526a6..e3b6843 100644
--- a/webrtc/media/BUILD.gn
+++ b/webrtc/media/BUILD.gn
@@ -117,10 +117,7 @@
     "sctp/sctpdataengine.h",
   ]
 
-  configs += [
-    "..:common_config",
-    ":rtc_media_warnings_config",
-  ]
+  configs += [ ":rtc_media_warnings_config" ]
 
   public_configs = [ "..:common_inherited_config" ]
 
@@ -250,10 +247,7 @@
       "engine/fakewebrtcvoiceengine.h",
     ]
 
-    configs += [
-      "..:common_config",
-      ":rtc_unittest_main_config",
-    ]
+    configs += [ ":rtc_unittest_main_config" ]
     public_configs = [ "..:common_inherited_config" ]
 
     if (rtc_build_libyuv) {
@@ -349,10 +343,7 @@
       "sctp/sctpdataengine_unittest.cc",
     ]
 
-    configs += [
-      "..:common_config",
-      ":rtc_media_unittests_config",
-    ]
+    configs += [ ":rtc_media_unittests_config" ]
     public_configs = [ "..:common_inherited_config" ]
 
     if (rtc_use_h264) {