This makes it clearer which modules set the channel.
Also remove GetChannel() from PeerConnection public API
This was only used once, internally, and can better be inlined.
Part of reducing the exposure of Channel.
Bug: webrtc:13931
Change-Id: I5f44865230a0d8314d269c85afb91d4b503e8de0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/260187
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36695}
19ebabc904