Remove webrtc/test/webrtc_test_common.gyp

Move the "webrtc_test_common" target to test.gyp and rename
it to "test_common".

Move all tests in "webrtc_test_common_unittests" (which
wasn't run on the bots) into "test_support_unittests".

NOTRY=True
NOPRESUBMIT=True

Review URL: https://codereview.webrtc.org/1754593002

Cr-Commit-Position: refs/heads/master@{#11848}
diff --git a/webrtc/modules/video_coding/video_coding_test.gypi b/webrtc/modules/video_coding/video_coding_test.gypi
index fc2fec6..8f7bc03 100644
--- a/webrtc/modules/video_coding/video_coding_test.gypi
+++ b/webrtc/modules/video_coding/video_coding_test.gypi
@@ -15,7 +15,7 @@
          'webrtc_video_coding',
          '<(DEPTH)/third_party/gflags/gflags.gyp:gflags',
          '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers_default',
-         '<(webrtc_root)/test/webrtc_test_common.gyp:webrtc_test_common',
+         '<(webrtc_root)/test/test.gyp:test_common',
       ],
       'sources': [
         # headers