Remove QualityScaler framerate reduction.

Framerate-reduction code is disabled on all platforms, and this code
adds complexity. It's necessary to react fast, especially on mobile
platforms or other bad network conditions and framerate reduction adds
another step between HD and QVGA.

BUG=webrtc:5678, webrtc:5830
R=jackychen@webrtc.org, mflodman@webrtc.org

Review URL: https://codereview.webrtc.org/1885893002 .

Cr-Commit-Position: refs/heads/master@{#12503}

webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc

@@ -598,15 +598,13 @@ int VP8EncoderImpl::InitEncode(const VideoCodec* inst,
   }
 
   rps_.Init();
-  // Disable both high-QP limits and framedropping. Both are handled by libvpx
-  // internally.
   // QP thresholds are chosen to be high enough to be hit in practice when
   // quality is good, but also low enough to not cause a flip-flop behavior
   // (e.g. going up in resolution shouldn't give so bad quality that we should
   // go back down).
   const int kLowQpThreshold = 29;
-  const int kDisabledBadQpThreshold = 100;
-  quality_scaler_.Init(kLowQpThreshold, kDisabledBadQpThreshold, false,
+  const int kBadQpThreshold = 100;
+  quality_scaler_.Init(kLowQpThreshold, kBadQpThreshold,
                        codec_.startBitrate, codec_.width, codec_.height,
                        codec_.maxFramerate);