Remove unused static VideoEncoder functions

BUG=None
TBR=stefan

Review-Url: https://codereview.webrtc.org/2967853002
Cr-Original-Commit-Position: refs/heads/master@{#18891}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: cc8856c9c29509d5c814495f61f489651a4c9f91
1 file changed