Clean away use of RtpAudioFeedback interface from RTP/RTCP receiver code.

webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h

Index: webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h
diff --git a/webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h b/webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h
index 2367a68d89ec5fcc3c347820b0a04e9f3ff5c5e3..9acef79f383ce13d2632643525ac55ed29773ddc 100644
--- a/webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h
+++ b/webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h
@@ -217,16 +217,6 @@ class RtpFeedback {
   virtual void OnIncomingCSRCChanged(const uint32_t CSRC, const bool added) = 0;
 };
 
-class RtpAudioFeedback {
- public:
-  virtual void OnPlayTelephoneEvent(const uint8_t event,
-                                    const uint16_t lengthMs,
-                                    const uint8_t volume) = 0;
-
- protected:
-  virtual ~RtpAudioFeedback() {}
-};
-
 class RtcpIntraFrameObserver {
  public:
   virtual void OnReceivedIntraFrameRequest(uint32_t ssrc) = 0;
@@ -357,16 +347,6 @@ class NullRtpData : public RtpData {
   }
 };
 
-// Null object version of RtpAudioFeedback.
-class NullRtpAudioFeedback : public RtpAudioFeedback {
- public:
-  virtual ~NullRtpAudioFeedback() {}
-
-  void OnPlayTelephoneEvent(const uint8_t event,
-                            const uint16_t lengthMs,
-                            const uint8_t volume) override {}
-};
-
 // Statistics about packet loss for a single directional connection. All values
 // are totals since the connection initiated.
 struct RtpPacketLossStats {