Remove unused method ExcludeFrameTypesToStr. Bug: webrtc:6634 Change-Id: I2816466ed428b8ce13f3073ca496c2891d5d6368 Reviewed-on: https://webrtc-review.googlesource.com/9400 Commit-Queue: Åsa Persson <asapersson@webrtc.org> Reviewed-by: Rasmus Brandt <brandtr@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20350}