Revert "Reset RtpFrameReferenceFinder on long pause"

This reverts commit 7a4db6eb0ef5a998019f03428072f0cc6afae866.

Reason for revert: Caused regression on perf tests.

Original change's description:
> Reset RtpFrameReferenceFinder on long pause
> 
> Bug: webrtc:11074
> Change-Id: I4c9a8761e9039d32885ccf9ac0eebdffdf67f48d
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/159240
> Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
> Reviewed-by: Erik Språng <sprang@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#29747}

TBR=ilnik@webrtc.org,sprang@webrtc.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: webrtc:11074
Change-Id: Ic40779087bf8e6bd94f02d38161f6abb9ca395f1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/159690
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29775}