Delete unneeded includes of deprecated system_wrappers include files.

webrtc/modules/audio_mixer/audio_mixer_impl.h

 /*
  *  Copyright (c) 2012 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.
  */
 
 #ifndef WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_IMPL_H_
 #define WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_IMPL_H_
 
 #include <memory>
 #include <vector>
 
 #include "webrtc/api/audio/audio_mixer.h"
 #include "webrtc/base/scoped_ref_ptr.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/base/race_checker.h"
 #include "webrtc/modules/audio_mixer/frame_combiner.h"
 #include "webrtc/modules/audio_mixer/output_rate_calculator.h"
 #include "webrtc/modules/audio_processing/include/audio_processing.h"
 #include "webrtc/modules/include/module_common_types.h"
-#include "webrtc/system_wrappers/include/critical_section_wrapper.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
 
 typedef std::vector<AudioFrame*> AudioFrameList;
 
 class AudioMixerImpl : public AudioMixer {
  public:
   struct SourceStatus {
     SourceStatus(Source* audio_source, bool is_mixed, float gain)
@@ skipping 75 matching lines @@
   SourceStatusList audio_source_list_ GUARDED_BY(crit_);  // May be mixed.
 
   // Component that handles actual adding of audio frames.
   FrameCombiner frame_combiner_ GUARDED_BY(race_checker_);
 
   RTC_DISALLOW_COPY_AND_ASSIGN(AudioMixerImpl);
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_IMPL_H_