Replace test_support_main by test_main and get rid of test_support_main_threaded_mac

test_support_main_threaded_mac doesn't seem to be used. It looks like it was
last used about a year and a half ago, and was removed in
https://webrtc-codereview.appspot.com/55379004

BUG=webrtc:6424
R=kjellander@webrtc.org
NOTRY=True

Review-Url: https://codereview.webrtc.org/2540693002
Cr-Commit-Position: refs/heads/master@{#15332}
diff --git a/webrtc/modules/BUILD.gn b/webrtc/modules/BUILD.gn
index 1708c15..3437e6e 100644
--- a/webrtc/modules/BUILD.gn
+++ b/webrtc/modules/BUILD.gn
@@ -74,8 +74,8 @@
       "../modules/video_coding",
       "../modules/video_coding:video_codecs_test_framework",
       "../system_wrappers",
+      "../test:test_main",
       "../test:test_support",
-      "../test:test_support_main",
       "//testing/gmock",
       "//testing/gtest",
     ]
@@ -649,8 +649,8 @@
       "../system_wrappers",
       "../test:rtp_test_utils",
       "../test:test_common",
+      "../test:test_main",
       "../test:test_support",
-      "../test:test_support_main",
       "../test:video_test_common",
       "audio_coding",
       "audio_coding:acm_receive_test",
@@ -750,7 +750,7 @@
       "..:webrtc_common",
       "../base:rtc_base_approved",
       "../test:test_common",
-      "../test:test_support_main",
+      "../test:test_main",
       "remote_bitrate_estimator:bwe_simulator_lib",
       "video_capture",
       "//testing/gmock",