Remove default implementation of PeerConnectionInterface::SetBitrate.

webrtc/api/peerconnectioninterface.h

Index: webrtc/api/peerconnectioninterface.h
diff --git a/webrtc/api/peerconnectioninterface.h b/webrtc/api/peerconnectioninterface.h
index 8ff7e1e469c7805e84eed4a0ec2eadb1c5874a23..64f5b2da6ec320862e5b478b1d3a2e92b3293c3e 100644
--- a/webrtc/api/peerconnectioninterface.h
+++ b/webrtc/api/peerconnectioninterface.h
@@ -742,9 +742,7 @@ class PeerConnectionInterface : public rtc::RefCountInterface {
   //
   // Setting |current_bitrate_bps| will reset the current bitrate estimate
   // to the provided value.
-  virtual RTCError SetBitrate(const BitrateParameters& bitrate) {
-    return RTCError::OK();
-  }
+  virtual RTCError SetBitrate(const BitrateParameters& bitrate) = 0;
 
   // Returns the current SignalingState.
   virtual SignalingState signaling_state() = 0;