Removed MediaStreamTrackInterface::set_state
The track state should be implicitly set by the underlying source.
This removes the public method and cleans up how AudioRtpReceiver is created. Further more it cleans up how the RtpReceivers are destroyed.

Note that this cl depend on https://codereview.webrtc.org/1790633002.
BUG=webrtc:5426

Review URL: https://codereview.webrtc.org/1816143002

Cr-Original-Commit-Position: refs/heads/master@{#12115}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: d61bf803d2949fb804c61a77c53ee9dd58c6d653
12 files changed