Remove deprecated OnKeyFrame method from video sink interface in media transport

Bug: webrtc:9719
Change-Id: I0d172e41bfe46ae4eec25de0e20f2ca4bfc64c19
Reviewed-on: https://webrtc-review.googlesource.com/c/120420
Reviewed-by: Anton Sukhanov <sukhanov@webrtc.org>
Commit-Queue: Peter Slatala <psla@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26454}
diff --git a/api/media_transport_interface.h b/api/media_transport_interface.h
index a46c994..1669b42 100644
--- a/api/media_transport_interface.h
+++ b/api/media_transport_interface.h
@@ -257,9 +257,6 @@
   // Called when new encoded video frame is received.
   virtual void OnData(uint64_t channel_id,
                       MediaTransportEncodedVideoFrame frame) = 0;
-
-  // TODO(bugs.webrtc.org/9719): Belongs on send side, not receive side.
-  RTC_DEPRECATED virtual void OnKeyFrameRequested(uint64_t channel_id) {}
 };
 
 // Interface for video sender to be notified of received key frame request.