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

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 57 matching lines @@
 
   // Parses the media specific parts of an RTP packet and updates the receiver
   // state. This for instance means that any changes in SSRC and payload type is
   // detected and acted upon.
   virtual bool IncomingRtpPacket(const RTPHeader& rtp_header,
                                  const uint8_t* payload,
                                  size_t payload_length,
                                  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;
   // Gets the time in milliseconds when the last timestamp was received.
   // Returns true if a packet has been received, false otherwise.
   virtual bool LastReceivedTimeMs(int64_t* receive_time_ms) const = 0;
 
   // Returns the remote SSRC of the currently received RTP stream.
   virtual uint32_t SSRC() const = 0;
 
   // Returns the current remote CSRCs.
   virtual int32_t CSRCs(uint32_t array_of_csrc[kRtpCsrcSize]) const = 0;
 
   // Returns the current energy of the RTP stream received.
   virtual int32_t Energy(uint8_t array_of_energy[kRtpCsrcSize]) const = 0;
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_RTP_RTCP_INCLUDE_RTP_RECEIVER_H_