Revert of Support external audio mixer.

webrtc/api/peerconnectionfactory.h

Index: webrtc/api/peerconnectionfactory.h
diff --git a/webrtc/api/peerconnectionfactory.h b/webrtc/api/peerconnectionfactory.h
index 4b412bacb9cc28e11897827f81adced8fa03a93e..7a30ab4569024879a336cd7dadcd378a77c7effe 100644
--- a/webrtc/api/peerconnectionfactory.h
+++ b/webrtc/api/peerconnectionfactory.h
@@ -111,8 +111,7 @@
       const rtc::scoped_refptr<webrtc::AudioDecoderFactory>&
           audio_decoder_factory,
       cricket::WebRtcVideoEncoderFactory* video_encoder_factory,
-      cricket::WebRtcVideoDecoderFactory* video_decoder_factory,
-      rtc::scoped_refptr<AudioMixer> audio_mixer);
+      cricket::WebRtcVideoDecoderFactory* video_decoder_factory);
   virtual ~PeerConnectionFactory();
 
  private:
@@ -136,9 +135,6 @@
   std::unique_ptr<cricket::WebRtcVideoDecoderFactory> video_decoder_factory_;
   std::unique_ptr<rtc::BasicNetworkManager> default_network_manager_;
   std::unique_ptr<rtc::BasicPacketSocketFactory> default_socket_factory_;
-  // External audio mixer. This can be NULL. In that case, internal audio mixer
-  // will be created and used.
-  rtc::scoped_refptr<AudioMixer> external_audio_mixer_;
 };
 
 }  // namespace webrtc