VP9 RTP frame reference finder cleanup.
VP9 RTP frame reference finder cleanup.

Bug: chromium:838402
Change-Id: Ib6117db5aeb83fc03f72759be2e42d0a4ceb94b6
Reviewed-on: https://webrtc-review.googlesource.com/60260
Reviewed-by: Stefan Holmer <eb0877843acc39f8ef6f7269937dee931c372d23@webrtc.org>
Reviewed-by: Niels Moller <0057859e47d61d90529d0f66d9ef692cefedb46a@webrtc.org>
Commit-Queue: Philip Eliasson <729b5e2dca9359bca8c81d600ef9d3e554586ac9@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#23139}
TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc