Remove OnLocalSsrcChanged and rename EncoderStateFeedback.

The renaming is to reflect this class is only used for RTCP interaction
and not for other transports.

This Cl will be followed by multiple CLs moving all send-side RTP
functionality to a separate class, rtp module ownership away from
VideoSendStream and use TaskQueue instead of ProcessThread for RTP.

BUG=webrtc:6456

Review-Url: https://codereview.webrtc.org/2390463002
Cr-Original-Commit-Position: refs/heads/master@{#14556}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 15d8357bab8d6a81417f7225408969f1514257ac
12 files changed