Removing the TFRC Rate Control

This removes the TRFC rate control which does not introduce any help in the
computation of the sending rate.
BUG=5083

Review URL: https://codereview.webrtc.org/1383813003

Cr-Original-Commit-Position: refs/heads/master@{#10299}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 757077b34e0cbcf0f6c5a3a1ba9303cb1d153a47