In some upcoming use cases we might wish to flush pending retransmissions from the pacer queue. In order to not make those packets forever inaccessible this CL adds a way to clear their "pending" status from the packet history. Bug: webrtc:11340 Change-Id: I9aac44125899a7f1e5a5e5be3390ac07b1e661ad Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/274600 Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Commit-Queue: Erik Språng <sprang@webrtc.org> Cr-Commit-Position: refs/heads/main@{#38037}