Remove differ from ScreenCapturer implementations

webrtc/modules/desktop_capture/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.
 
 import("//build/config/ui.gni")
 import("../../build/webrtc.gni")
@@ skipping 106 matching lines @@
   if (!is_win && !is_mac && !use_x11) {
     sources += [
       "mouse_cursor_monitor_null.cc",
       "screen_capturer_null.cc",
       "window_capturer_null.cc",
     ]
   }
 
   if (!is_ios) {
     sources += [
-      "differ.cc",
-      "differ.h",
       "differ_block.cc",
       "differ_block.h",
       "screen_capturer_differ_wrapper.cc",
       "screen_capturer_differ_wrapper.h",
     ]
   }
 
   if (is_mac) {
     libs = [
       "AppKit.framework",
@@ skipping 34 matching lines @@
     sources = [
       "differ_vector_sse2.cc",
       "differ_vector_sse2.h",
     ]
 
     if (is_posix) {
       cflags = [ "-msse2" ]
     }
   }
 }