Reland "Avoid sending empty receiver reports with RtcpTransceiver"

This reverts commit 48420fa947cea4c618d51dc5f87908765a3a69db.

Reason for revert: downstream unittests adjusted

Original change's description:
> Revert "Avoid sending empty receiver reports with RtcpTransceiver"
>
> This reverts commit e5f1a3992e3bbfa0445b90f317576c8229524d74.
>
> Reason for revert: Speculative revert due to failing downstream unittest.
>
> Original change's description:
> > Avoid sending empty receiver reports with RtcpTransceiver
> >
> > Bug: None
> > Change-Id: Ia017c2df285febefb72ba88ba43366455bde5a78
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/222402
> > Reviewed-by: Per Kjellander <perkj@webrtc.org>
> > Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
> > Cr-Commit-Position: refs/heads/master@{#34281}
>
> TBR=danilchap@webrtc.org,perkj@webrtc.org,webrtc-scoped@luci-project-accounts.iam.gserviceaccount.com
>
> Change-Id: I895317ad0381756e97e501a36d6440f83a68b6f8
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: None
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/222440
> Reviewed-by: Björn Terelius <terelius@webrtc.org>
> Commit-Queue: Björn Terelius <terelius@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#34284}

# Not skipping CQ checks because this is a reland.

Bug: None
Change-Id: I3481b9b12ddabaef7303ba80e9cd885930988caa
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/222600
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34291}