Replaces the VP8 simulcast index and VP9 spatial index formely part of CodecSpecificInfo. Bug: webrtc:9378 Change-Id: I80eafd63fbdee0a25864338196a690628b4bd3d2 Reviewed-on: https://webrtc-review.googlesource.com/83161 Commit-Queue: Niels Moller <nisse@webrtc.org> Reviewed-by: Erik Språng <sprang@webrtc.org> Reviewed-by: Sebastian Jansson <srte@webrtc.org> Reviewed-by: Magnus Jedvert <magjed@webrtc.org> Reviewed-by: Philip Eliasson <philipel@webrtc.org> Reviewed-by: Rasmus Brandt <brandtr@webrtc.org> Cr-Commit-Position: refs/heads/master@{#24485}