Remove use of PCH files in webrtc/sdk/objc

webrtc/BUILD.gn

 # Copyright (c) 2014 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.
 
 # TODO(kjellander): Rebase this to webrtc/build/common.gypi changes after r6330.
 
@@ skipping 197 matching lines @@
   }
 
   if (use_libfuzzer || use_drfuzz || use_afl) {
     # Used in Chromium's overrides to disable logging
     defines += [ "WEBRTC_UNSAFE_FUZZER_MODE" ]
   }
 }
 
 config("common_objc") {
   libs = [ "Foundation.framework" ]
-  precompiled_header = "sdk/objc/WebRTC-Prefix.pch"
-  precompiled_source = "sdk/objc/WebRTC-Prefix.pch"
 }
 
 if (!build_with_chromium) {
   # Target to build all the WebRTC production code.
   rtc_static_library("webrtc") {
     # Only the root target should depend on this.
     visibility = [ "//:default" ]
 
     sources = [
       # TODO(kjellander): Remove this whenever possible. GN's static_library
@@ skipping 479 matching lines @@
       ]
 
       deps = [
         "//base:base_java_test_support",
         "//webrtc/examples:AppRTCMobile_javalib",
         "//webrtc/sdk/android:libjingle_peerconnection_java",
       ]
     }
   }
 }