Properly clean up RtpVideoSender.

Bug: webrtc:9517
Change-Id: I625c132907bd178f62c8b99f4b2407c75aa7e947
Reviewed-on: https://webrtc-review.googlesource.com/89382
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Stefan Holmer <stefan@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24022}

call/rtp_transport_controller_send_interface.h

@@ -100,6 +100,8 @@ class RtpTransportControllerSendInterface {
       Transport* send_transport,
       const RtpSenderObservers& observers,
       RtcEventLog* event_log) = 0;
+  virtual void DestroyVideoRtpSender(
+      VideoRtpSenderInterface* rtp_video_sender) = 0;
 
   virtual TransportFeedbackObserver* transport_feedback_observer() = 0;