Revert of Implemented the GetSources() in native code.

webrtc/audio/audio_receive_stream.cc

Index: webrtc/audio/audio_receive_stream.cc
diff --git a/webrtc/audio/audio_receive_stream.cc b/webrtc/audio/audio_receive_stream.cc
index cb90a68a0f72e6898fe11726d31d2b99c9770c98..fbd61ccfd4791e3386a9cd68565c053782fe2616 100644
--- a/webrtc/audio/audio_receive_stream.cc
+++ b/webrtc/audio/audio_receive_stream.cc
@@ -219,11 +219,6 @@
   channel_proxy_->SetChannelOutputVolumeScaling(gain);
 }
 
-std::vector<RtpSource> AudioReceiveStream::GetSources() const {
-  RTC_DCHECK_RUN_ON(&worker_thread_checker_);
-  return channel_proxy_->GetSources();
-}
-
 AudioMixer::Source::AudioFrameInfo AudioReceiveStream::GetAudioFrameWithInfo(
     int sample_rate_hz,
     AudioFrame* audio_frame) {