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/webrtc/audio/audio_sink.h b/webrtc/audio/audio_sink.h
index 50ce7a1..999644f 100644
--- a/webrtc/audio/audio_sink.h
+++ b/webrtc/audio/audio_sink.h
@@ -19,12 +19,10 @@
 #include <inttypes.h>
 #include <stddef.h>
 
-#include "webrtc/base/refcount.h"
-
 namespace webrtc {
 
 // Represents a simple push audio sink.
-class AudioSinkInterface : public rtc::RefCountInterface {
+class AudioSinkInterface {
  public:
   virtual ~AudioSinkInterface() {}