Revert of Storing raw audio sink for default audio track. (patchset #7 id:120001 of https://codereview.chromium.org/1551813002/ )

Reason for revert:
tommi pointed out that using a refptr for the sink may cause issues. Will reland with a slightly different approach.

Original issue's description:
> Storing raw audio sink for default audio track.
>
> BUG=webrtc:5250
>
> Committed: https://crrev.com/e591f9377f33f3f725a30faecd1bef1a71fa6b99
> Cr-Commit-Position: refs/heads/master@{#11230}

TBR=pthatcher@webrtc.org,solenberg@webrtc.org,pbos@webrtc.org,tommi@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:5250

Review URL: https://codereview.webrtc.org/1588693002

Cr-Commit-Position: refs/heads/master@{#11241}
diff --git a/talk/session/media/channel.h b/talk/session/media/channel.h
index 4cfefd8..d8fde67 100644
--- a/talk/session/media/channel.h
+++ b/talk/session/media/channel.h
@@ -375,9 +375,8 @@
   // event 0-9, *, #, A-D.
   bool InsertDtmf(uint32_t ssrc, int event_code, int duration);
   bool SetOutputVolume(uint32_t ssrc, double volume);
-  void SetRawAudioSink(
-      uint32_t ssrc,
-      const rtc::scoped_refptr<webrtc::AudioSinkInterface>& sink);
+  void SetRawAudioSink(uint32_t ssrc,
+                       rtc::scoped_ptr<webrtc::AudioSinkInterface> sink);
 
   // Get statistics about the current media session.
   bool GetStats(VoiceMediaInfo* stats);