Reason for revert:
Breaks fuzzer compilation.
Original issue's description:
> Make rtcp parsing implementation private in RtcpReceiver:
> Function just for Parse and for Callbacks moved to private section.
> All handles moved from protected to private section.
>
> BUG=webrtc:5260
> R=sprang@webrtc.org
>
> Committed: https://crrev.com/faf708e238c7b43a732fbebf79ac9298b4b95a95
> Cr-Commit-Position: refs/heads/master@{#14181}
TBR=sprang@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:5260
Review-Url: https://codereview.webrtc.org/2332673003
Cr-Commit-Position: refs/heads/master@{#14182}
180e4525ca