Deprecate VideoDecoder::Reset() and remove calls.

Removes calls to decoder reset and instead drops delta frames and
requests keyframes until one arrives.

BUG=webrtc:5475
R=stefan@webrtc.org
TBR=mflodman@webrtc.org

Review URL: https://codereview.webrtc.org/1647163002 .

Cr-Original-Commit-Position: refs/heads/master@{#11460}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: ed3277bf140d2250f2f735c89d3a2c628454f8fa
23 files changed