Removing some old code which looked like it had to do with NACK handling but in reality did nothing.

webrtc/modules/rtp_rtcp/include/rtp_receiver.h

Index: webrtc/modules/rtp_rtcp/include/rtp_receiver.h
diff --git a/webrtc/modules/rtp_rtcp/include/rtp_receiver.h b/webrtc/modules/rtp_rtcp/include/rtp_receiver.h
index f393e41eabd6110afc1f685c333f6bb21556d05b..9db1c63da78976d554d8530e916f017cf99a66be 100644
--- a/webrtc/modules/rtp_rtcp/include/rtp_receiver.h
+++ b/webrtc/modules/rtp_rtcp/include/rtp_receiver.h
@@ -75,12 +75,6 @@ class RtpReceiver {
                                  PayloadUnion payload_specific,
                                  bool in_order) = 0;
 
-  // Returns the currently configured NACK method.
-  virtual NACKMethod NACK() const = 0;
-
-  // Turn negative acknowledgement (NACK) requests on/off.
-  virtual void SetNACKStatus(const NACKMethod method) = 0;
-
   // Gets the last received timestamp. Returns true if a packet has been
   // received, false otherwise.
   virtual bool Timestamp(uint32_t* timestamp) const = 0;