Get rid of unnecessary cast of FlexfecReceiveStreamImpl to FlexfecReceiveStream

webrtc/call/flexfec_receive_stream_impl.h

Index: webrtc/call/flexfec_receive_stream_impl.h
diff --git a/webrtc/call/flexfec_receive_stream_impl.h b/webrtc/call/flexfec_receive_stream_impl.h
index 81c09d6fac79b3c91d2f0ad7f694310bc73d5590..de5de4190ccbda08722732b14e02659cac103513 100644
--- a/webrtc/call/flexfec_receive_stream_impl.h
+++ b/webrtc/call/flexfec_receive_stream_impl.h
@@ -40,8 +40,6 @@ class FlexfecReceiveStreamImpl : public FlexfecReceiveStream,
       ProcessThread* process_thread);
   ~FlexfecReceiveStreamImpl() override;
 
-  const Config& GetConfig() const { return config_; }
-
   // RtpPacketSinkInterface.
   void OnRtpPacket(const RtpPacketReceived& packet) override;
 
@@ -49,6 +47,7 @@ class FlexfecReceiveStreamImpl : public FlexfecReceiveStream,
   void Start() override;
   void Stop() override;
   Stats GetStats() const override;
+  const Config& GetConfig() const override;
 
  private:
   // Config.