GN: Move variables from //build_overrides/webrtc.gni to //webrtc/build/webrtc.gni

webrtc/sdk/BUILD.gn

 # Copyright 2016 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("../build/webrtc.gni")
-import("//build_overrides/webrtc.gni")
 import("//build/config/mac/mac_sdk.gni")
 
 if (is_ios || (is_mac && mac_deployment_target == "10.7")) {
   config("rtc_sdk_common_objc_config") {
     include_dirs = [
       "objc/Framework/Classes",
       "objc/Framework/Headers",
     ]
   }
 
@@ skipping 186 matching lines @@
     if (rtc_build_libyuv) {
       deps += [ "$rtc_libyuv_dir" ]
       public_deps = [
         "$rtc_libyuv_dir",
       ]
     }
   }
 
   # TODO(tkchin): Add the rtc_sdk_framework_objc target.
 }