Remove StreamStatistician::IsPacketInOrder

this function is now only used in combination with StreamStatistician::IsRetransmitOfOldPacket
but IsRetransmitOfOldPacket internally checks if packet is in_order, thus making extra check unnecessary

In addition to making code simpler, removing this checks avoids
taking two extra CritSection on common code path of incoming rtp packet.

Bug: webrtc:8016
Change-Id: I050004e256b5698ce700e3416aa86b55f446a270
Reviewed-on: https://webrtc-review.googlesource.com/85361
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23762}
diff --git a/video/rtp_video_stream_receiver.h b/video/rtp_video_stream_receiver.h
index 75dcea5..083bb36 100644
--- a/video/rtp_video_stream_receiver.h
+++ b/video/rtp_video_stream_receiver.h
@@ -150,8 +150,7 @@
                                          const RTPHeader& header);
   void NotifyReceiverOfEmptyPacket(uint16_t seq_num);
   void NotifyReceiverOfFecPacket(const RTPHeader& header);
-  bool IsPacketInOrder(const RTPHeader& header) const;
-  bool IsPacketRetransmitted(const RTPHeader& header, bool in_order) const;
+  bool IsPacketRetransmitted(const RTPHeader& header) const;
   void UpdateHistograms();
   bool IsRedEnabled() const;
   void InsertSpsPpsIntoTracker(uint8_t payload_type);