Revert "Wiring the RTCRtpEncodingParameters.priority down to the bitrate allocator."

This reverts commit d2b912aed132c751919ed286439fb39bbd714dda.

Reason for revert: broke internal tests

Original change's description:
> Wiring the RTCRtpEncodingParameters.priority down to the bitrate allocator.
> 
> I followed the wiring path for the max bitrate.
> Doc:
> https://docs.google.com/a/google.com/document/d/1sGT6y00prOIErFuGD44zWZacDpR6Rkjg_HXA_Z3Vw4Q/edit?usp=sharing
> 
> Bug: webrtc:8630
> Change-Id: I6b861816670442656721c20f81d035ee5eb6218c
> Reviewed-on: https://webrtc-review.googlesource.com/30380
> Commit-Queue: Seth Hampson <shampson@webrtc.org>
> Reviewed-by: Stefan Holmer <stefan@webrtc.org>
> Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
> Reviewed-by: Erik Språng <sprang@webrtc.org>
> Reviewed-by: Elad Alon <eladalon@webrtc.org>
> Reviewed-by: Peter Thatcher <pthatcher@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#21397}

TBR=solenberg@webrtc.org,eladalon@webrtc.org,sprang@webrtc.org,stefan@webrtc.org,pthatcher@webrtc.org,shampson@webrtc.org

Change-Id: If82810072e21818ae452a0fc3f984d44e5dac70c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:8630
Reviewed-on: https://webrtc-review.googlesource.com/35540
Reviewed-by: Lu Liu <lliuu@webrtc.org>
Commit-Queue: Lu Liu <lliuu@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21399}

test/encoder_settings.cc

@@ -55,7 +55,6 @@ std::vector<VideoStream> CreateVideoStreams(
 
   stream_settings[encoder_config.number_of_streams - 1].max_bitrate_bps +=
       bitrate_left_bps;
-  stream_settings[0].bitrate_priority = encoder_config.bitrate_priority;
 
   return stream_settings;
 }