Revert of GN: Enable ARC for Mac and iOS in rtc_* templates

webrtc/webrtc.gni

Index: webrtc/webrtc.gni
diff --git a/webrtc/webrtc.gni b/webrtc/webrtc.gni
index e47ac08afcca21a6a37267a157a1a60a4f446b00..6f902c97bf393c9b27673fc425d2b0bfa5663c63 100644
--- a/webrtc/webrtc.gni
+++ b/webrtc/webrtc.gni
@@ -210,10 +210,6 @@
 # both for WebRTC stand-alone builds and for the scenario when WebRTC
 # native code is built as part of Chromium.
 rtc_common_configs = [ webrtc_root + ":common_config" ]
-
-if (is_mac || is_ios) {
-  rtc_common_configs += [ "//build/config/compiler:enable_arc" ]
-}
 
 # Global public configuration that should be applied to all WebRTC targets. You
 # normally shouldn't need to include this in your target as it's automatically