Remove VCMRenderBufferSizeCallback.

Unused/dead code.

BUG=
R=stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1923713002 .

Cr-Commit-Position: refs/heads/master@{#12595}

webrtc/modules/video_coding/include/video_coding_defines.h

@@ -199,16 +199,6 @@ class VCMQMSettingsCallback {
   virtual ~VCMQMSettingsCallback() {}
 };
 
-// Callback class used for telling the user about the size (in time) of the
-// render buffer, that is the size in time of the complete continuous frames.
-class VCMRenderBufferSizeCallback {
- public:
-  virtual void RenderBufferSizeMs(int buffer_size_ms) = 0;
-
- protected:
-  virtual ~VCMRenderBufferSizeCallback() {}
-};
-
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_INCLUDE_VIDEO_CODING_DEFINES_H_