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

webrtc/modules/audio_device/BUILD.gn

Index: webrtc/modules/audio_device/BUILD.gn
diff --git a/webrtc/modules/audio_device/BUILD.gn b/webrtc/modules/audio_device/BUILD.gn
index 9c776d38913f0610e64cbeb39ce0901137930b39..8c7f7ba4c36c899132d6bccaef0e81c0aeb9d22d 100644
--- a/webrtc/modules/audio_device/BUILD.gn
+++ b/webrtc/modules/audio_device/BUILD.gn
@@ -198,8 +198,6 @@ rtc_static_library("audio_device") {
           "ios/voice_processing_audio_unit.h",
           "ios/voice_processing_audio_unit.mm",
         ]
-        configs += [ "//build/config/compiler:enable_arc" ]
-
         libs = [
           "AudioToolbox.framework",
           "AVFoundation.framework",
@@ -297,7 +295,6 @@ if (rtc_include_tests) {
     }
     if (is_ios) {
       sources += [ "ios/objc/RTCAudioSessionTest.mm" ]
-      configs += [ "//build/config/compiler:enable_arc" ]
       if (target_cpu != "x64") {
         sources += [ "ios/audio_device_unittest_ios.cc" ]
       }