Reland of move unused build override

build/config/mac/mac_sdk.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/chrome_build.gni")
 import("//build/toolchain/toolchain.gni")
 
 # See https://bugs.chromium.org/p/webrtc/issues/detail?id=5453.
 # We can drop the rtc_require_mac_10_7_deployment flag when Chromium
 # also requires a 10.7 deployment target.
 import("//build_overrides/build.gni")
 
 declare_args() {
   # Minimum supported version of the Mac SDK.
   mac_sdk_min = mac_sdk_min_build_override
 
   # Minimum supported version of OSX.
-  mac_deployment_target = mac_deployment_target_build_override
+  mac_deployment_target = "10.9"
 
   # Path to a specific version of the Mac SDK, not including a slash at the end.
   # If empty, the path to the lowest version greater than or equal to
   # mac_sdk_min is used.
   mac_sdk_path = ""
 
   # The SDK name as accepted by xcodebuild.
   mac_sdk_name = "macosx"
 }
 
@@ skipping 67 matching lines @@
       "          either upgrade Xcode to the latest version or install the Mac OS X")
   print(
       "          $mac_sdk_min_build_override SDK. For more information, see https://crbug.com/620127.")
   print()
   print(" Current SDK Version:   $mac_sdk_version")
   print(" Current Xcode Version: $xcode_version ($xcode_build)")
   print(
       "********************************************************************************")
   assert(false, "SDK is incompatible with Xcode")
 }