Delete VCMSendStatisticsCallback and corresponding use of ProcessThread

Bug: webrtc:8422
Change-Id: I5863266a0226d475c4fdd810f2f6f1acdf922df3
Reviewed-on: https://webrtc-review.googlesource.com/14880
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20440}

modules/video_coding/include/video_coding_defines.h

@@ -84,16 +84,6 @@ class VCMReceiveCallback {
   virtual ~VCMReceiveCallback() {}
 };
 
-// Callback class used for informing the user of the bit rate and frame rate,
-// and the name of the encoder.
-class VCMSendStatisticsCallback {
- public:
-  virtual void SendStatistics(uint32_t bitRate, uint32_t frameRate) = 0;
-
- protected:
-  virtual ~VCMSendStatisticsCallback() {}
-};
-
 // Callback class used for informing the user of the incoming bit rate and frame
 // rate.
 class VCMReceiveStatisticsCallback {