Remove GetSendSideDelay from RtpRtcp.

These stats are reported using a callback either way, removing a getter
+ an old related deadlock suppression.

BUG=1695, 2999
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/50119004

Cr-Commit-Position: refs/heads/master@{#9314}

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.h

@@ -122,9 +122,6 @@ class ModuleRtpRtcpImpl : public RtpRtcp {
   // less than |bytes|.
   size_t TimeToSendPadding(size_t bytes) override;
 
-  bool GetSendSideDelay(int* avg_send_delay_ms,
-                        int* max_send_delay_ms) const override;
-
   // RTCP part.
 
   // Get RTCP status.