As a bonus, we also get rid of most uses of CodecInst in voe::Channel.
BUG=webrtc:8396
Change-Id: I20f82274dcec2ad8be6e046b987d7d65a19d0e46
Reviewed-on: https://webrtc-review.googlesource.com/10802
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20354}