Remove the VoiceEngineObserver callback interface.

media/engine/fakewebrtcvoiceengine.h

 /*
  *  Copyright (c) 2010 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.
  */
 
@@ skipping 39 matching lines @@
   bool IsInited() const { return inited_; }
   int GetLastChannel() const { return last_channel_; }
   int GetNumChannels() const { return static_cast<int>(channels_.size()); }
   void set_fail_create_channel(bool fail_create_channel) {
     fail_create_channel_ = fail_create_channel;
   }
 
   WEBRTC_STUB(Release, ());
 
   // webrtc::VoEBase
-  WEBRTC_STUB(RegisterVoiceEngineObserver, (
-      webrtc::VoiceEngineObserver& observer));
-  WEBRTC_STUB(DeRegisterVoiceEngineObserver, ());
   WEBRTC_FUNC(Init,
               (webrtc::AudioDeviceModule* adm,
                webrtc::AudioProcessing* audioproc,
                const rtc::scoped_refptr<webrtc::AudioDecoderFactory>&
                    decoder_factory)) {
     inited_ = true;
     return 0;
   }
   WEBRTC_FUNC(Terminate, ()) {
     inited_ = false;
@@ skipping 47 matching lines @@
   std::map<int, Channel*> channels_;
   bool fail_create_channel_ = false;
   webrtc::voe::TransmitMixer* transmit_mixer_ = nullptr;
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(FakeWebRtcVoiceEngine);
 };
 
 }  // namespace cricket
 
 #endif  // MEDIA_ENGINE_FAKEWEBRTCVOICEENGINE_H_