Making RemoteBitrateEstimator to be ReceiveSideCC implementation detail allows code to be cleaner. Bug: None Change-Id: I1d3327c44b364c6c2a1005391cf1dc468e0cc8ce Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/266482 Reviewed-by: Philip Eliasson <philipel@webrtc.org> Reviewed-by: Niels Moller <nisse@webrtc.org> Commit-Queue: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/main@{#37305}