Delete unused support for vp8 partitions.

This also makes it possible to drop the RTPFragmentationHeader from
the class VCMEncodedFrame.

BUG=None

Review-Url: https://codereview.webrtc.org/2380933003
Cr-Commit-Position: refs/heads/master@{#14455}

webrtc/modules/video_coding/frame_buffer.cc

@@ -253,18 +253,8 @@ bool VCMFrameBuffer::IsRetransmitted() const {
 }
 
 void VCMFrameBuffer::PrepareForDecode(bool continuous) {
-#ifdef INDEPENDENT_PARTITIONS
-  if (_codec == kVideoCodecVP8) {
-    _length = _sessionInfo.BuildVP8FragmentationHeader(_buffer, _length,
-                                                       &_fragmentation);
-  } else {
-    size_t bytes_removed = _sessionInfo.MakeDecodable();
-    _length -= bytes_removed;
-  }
-#else
   size_t bytes_removed = _sessionInfo.MakeDecodable();
   _length -= bytes_removed;
-#endif
   // Transfer frame information to EncodedFrame and create any codec
   // specific information.
   _frameType = _sessionInfo.FrameType();