[Cast] Clean-up: Move max_unacked_frames into CongestionControl.

media/cast/sender/frame_sender.h

Index: media/cast/sender/frame_sender.h
diff --git a/media/cast/sender/frame_sender.h b/media/cast/sender/frame_sender.h
index 0e8595d213493762a26970dfaca6b576d9d4cfc3..a3ef1e55119e559bb6f76bb1f776ad741aeea543 100644
--- a/media/cast/sender/frame_sender.h
+++ b/media/cast/sender/frame_sender.h
@@ -125,10 +125,6 @@ class FrameSender {
   // Max encoded frames generated per second.
   double max_frame_rate_;
 
-  // Maximum number of outstanding frames before the encoding and sending of
-  // new frames shall halt.
-  int max_unacked_frames_;
-
   // Counts how many RTCP reports are being "aggressively" sent (i.e., one per
   // frame) at the start of the session.  Once a threshold is reached, RTCP
   // reports are instead sent at the configured interval + random drift.