Delete unused method SetSelectiveRetransmissions

Bug: None
Change-Id: I5a59b5776fe537ec380629f9e5e9ac98c9e1214b
Reviewed-on: https://webrtc-review.googlesource.com/c/119920
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26407}

modules/rtp_rtcp/source/rtp_rtcp_impl.h

@@ -232,10 +232,6 @@ class ModuleRtpRtcpImpl : public RtpRtcp, public RTCPReceiver::ModuleRtpRtcp {
 
   // (NACK) Negative acknowledgment part.
 
-  int SelectiveRetransmissions() const override;
-
-  int SetSelectiveRetransmissions(uint8_t settings) override;
-
   // Send a Negative acknowledgment packet.
   // TODO(philipel): Deprecate SendNACK and use SendNack instead.
   int32_t SendNACK(const uint16_t* nack_list, uint16_t size) override;