Delete unused method RtpRtcp::GetRtpPacketLossStats

It was introduced, together with the PacketLossStats class, in cl
https://codereview.webrtc.org/1198853004 (#9568). It is unused in webrtc,
but there's downstream usage of the PacketLossStats class, which
should perhaps be moved or deleted in a later cl.

Bug: None
Change-Id: I17a3d5c8748f2cc9809c438630cbe8ab680466c4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/140042
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28153}

modules/rtp_rtcp/include/rtp_rtcp.h

@@ -337,12 +337,6 @@ class RtpRtcp : public Module, public RtcpFeedbackSenderInterface {
       StreamDataCounters* rtp_counters,
       StreamDataCounters* rtx_counters) const = 0;
 
-  // Returns packet loss statistics for the RTP stream.
-  virtual void GetRtpPacketLossStats(
-      bool outgoing,
-      uint32_t ssrc,
-      struct RtpPacketLossStats* loss_stats) const = 0;
-
   // Returns received RTCP report block.
   // Returns -1 on failure else 0.
   // TODO(https://crbug.com/webrtc/10678): Remove this in favor of