Delete support for sending RTCP RPSI and SLI messages.

BUG=webrtc:7338

Review-Url: https://codereview.webrtc.org/2746413003
Cr-Original-Commit-Position: refs/heads/master@{#17229}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: cd386eb13fdc2420a0e6811ec2beca2d553f2166
14 files changed