Drop stale payload types in SetReceiveCodecs()

ChannelReceive::SetReceiveCodecs() adds entries to
payload_type_frequencies_ but never removes any, while payload_type_map_
and the NetEq decoders are replaced. After a renegotiation removes a
payload type, packets with that payload type still pass the filter in
OnRtpPacket(). They update the NACK tracker and the receive statistics,
and are only rejected later by NetEq.

Rebuild the map on every call so that it matches the negotiated codecs.

Bug: none
Change-Id: I1443aa2ce88efbd91eb10b5aef36f49d290755d1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/506981
Auto-Submit: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Jakob Ivarsson‎ <jakobi@webrtc.org>
Commit-Queue: Jakob Ivarsson‎ <jakobi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48790}