Removes unused reserved bitrate in BitrateController.

This removes the reserved bitrate feature as it is not currently used.
This saves debugging time as there is less code to investigate. This
also makes it easier to compare the code with the task queue based
version which lacks this feature.

Bug: webrtc:9586
Change-Id: I207624ceb8d203c88c3d01bfc753d60523f99fe4
Reviewed-on: https://webrtc-review.googlesource.com/92622
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24357}

modules/bitrate_controller/include/bitrate_controller.h

@@ -92,8 +92,6 @@ class BitrateController : public Module, public RtcpBandwidthObserver {
   // this bandwidth excludes packet headers.
   virtual bool AvailableBandwidth(uint32_t* bandwidth) const = 0;
 
-  virtual void SetReservedBitrate(uint32_t reserved_bitrate_bps) = 0;
-
   virtual bool GetNetworkParameters(uint32_t* bitrate,
                                     uint8_t* fraction_loss,
                                     int64_t* rtt) = 0;