Revert "Convert native handles to buffers before encoding."

This reverts commit a831dc3a7d10a1fbaa258ee6b1ca6cfc7e91c5ca to unblock
rolling into Chromium.

BUG=4081
TBR=magjed@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/55549004

Cr-Commit-Position: refs/heads/master@{#9354}

webrtc/modules/video_coding/main/source/generic_encoder.h

@@ -138,8 +138,6 @@ public:
 
     void OnDroppedFrame();
 
-    bool SupportsNativeHandle() const;
-
 private:
     VideoEncoder* const encoder_;
     VideoEncoderRateObserver* const rate_observer_;