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}
7 files changed