This simplifies configuration, and it is a preparation for replaceing
encoder instance with an encoder factory in
VideoSendStream::Config::EncoderSettings.
Bug: webrtc:8830
Change-Id: Iaf4f6ad9e7cfaa76d8600c4fa68f393e2f3ea331
Reviewed-on: https://webrtc-review.googlesource.com/69809
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22859}