Delete unused methods SetStartImage and SetTimeoutImage.

Declared in webrtc::VideoRender, implemented in IncomingVideoStream.
This cl also eliminates some of the few uses of
webrtc::VideoFrame::CopyFrame.

BUG=webrtc:5682

Review URL: https://codereview.webrtc.org/1885323002

Cr-Original-Commit-Position: refs/heads/master@{#12427}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: cc23b7c1ea33a252736986e2d3089215f78a6794
6 files changed