Reason for revert:
A few perf tests broken, including
RampUpTest.UpDownUpAbsSendTimeSimulcastRedRtx
RampUpTest.UpDownUpTransportSequenceNumberRtx
RampUpTest.UpDownUpTransportSequenceNumberPacketLoss
Original issue's description:
> Use RtxReceiveStream.
>
> This also has the beneficial side-effect that when a media stream
> which is protected by FlexFEC receives an RTX retransmission, the
> retransmitted media packet is passed into the FlexFEC machinery,
> which should improve its ability to recover packets via FEC.
>
> BUG=webrtc:7135
>
> Review-Url: https://codereview.webrtc.org/3008773002
> Cr-Commit-Position: refs/heads/master@{#19649}
> Committed: 5c0f6c62eaTBR=brandtr@webrtc.org,danilchap@webrtc.org,stefan@webrtc.org,magjed@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:7135
Review-Url: https://codereview.webrtc.org/3010983002
Cr-Commit-Position: refs/heads/master@{#19653}
3c39c0137a