Remove non-implemented function signatures from RtpFrameReferenceFinder.
Remove non-implemented function signatures from RtpFrameReferenceFinder.

Bug: none
Change-Id: I17e7cb6300cc6f4c82517d6a2059c7be6d4fb9ad
Reviewed-on: https://webrtc-review.googlesource.com/86882
Reviewed-by: Danil Chapovalov <55de8d9c2b5977da2dd48f967f21f9d606b172a5@webrtc.org>
Commit-Queue: Philip Eliasson <729b5e2dca9359bca8c81d600ef9d3e554586ac9@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#23832}
ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc