Remove remaining quality-analysis (QM).

This was never turned on, contains a lot of complexity and somehow
manages triggering a bug in a downstream project.

BUG=webrtc:5066
R=marpan@webrtc.org
TBR=mflodman@webrtc.org

Review URL: https://codereview.webrtc.org/1917323002 .

Cr-Commit-Position: refs/heads/master@{#12692}

webrtc/modules/video_processing/include/video_processing.h

@@ -53,9 +53,6 @@ class VideoProcessing {
 
   virtual void EnableDenoising(bool enable) = 0;
   virtual const VideoFrame* PreprocessFrame(const VideoFrame& frame) = 0;
-
-  virtual VideoContentMetrics* GetContentMetrics() const = 0;
-  virtual void EnableContentAnalysis(bool enable) = 0;
 };
 
 }  // namespace webrtc