Revert of Support external audio mixer.

webrtc/media/engine/webrtcvoiceengine.h

Index: webrtc/media/engine/webrtcvoiceengine.h
diff --git a/webrtc/media/engine/webrtcvoiceengine.h b/webrtc/media/engine/webrtcvoiceengine.h
index 4032814705565e409ed86223b0c771fe0f2aca78..03b493744b857f903cbb09f530794787466e7b8f 100644
--- a/webrtc/media/engine/webrtcvoiceengine.h
+++ b/webrtc/media/engine/webrtcvoiceengine.h
@@ -34,7 +34,6 @@
 namespace cricket {
 
 class AudioDeviceModule;
-class AudioMixer;
 class AudioSource;
 class VoEWrapper;
 class WebRtcVoiceMediaChannel;
@@ -49,13 +48,11 @@
 
   WebRtcVoiceEngine(
       webrtc::AudioDeviceModule* adm,
-      const rtc::scoped_refptr<webrtc::AudioDecoderFactory>& decoder_factory,
-      rtc::scoped_refptr<webrtc::AudioMixer> audio_mixer);
+      const rtc::scoped_refptr<webrtc::AudioDecoderFactory>& decoder_factory);
   // Dependency injection for testing.
   WebRtcVoiceEngine(
       webrtc::AudioDeviceModule* adm,
       const rtc::scoped_refptr<webrtc::AudioDecoderFactory>& decoder_factory,
-      rtc::scoped_refptr<webrtc::AudioMixer> audio_mixer,
       VoEWrapper* voe_wrapper);
   ~WebRtcVoiceEngine() override;