Revert 232493 "Update libvpx"

It introduced a new textrel: vp9_loop_filter_horizontal_edge_mmx

> Update libvpx
> 
> Pull latest version from upstream. This had to be broken up across several
> changes. The first has the commit message:
> https://codereview.chromium.org/55493002/
> 
> Remove AVX code until we update the gyp files:
> https://codereview.chromium.org/48903015/
> 
> libmkv has moved to third_party/libmkv:
> https://codereview.chromium.org/54373014/
> media/webm/chromeos/webm_encoder.cc and
> media/webm/chromeon/ebml_writer.cc pull from this location
> as well and needs to be updated.
> 
> R=fischman@chromium.org, tomfinegan@chromium.org
> 
> Review URL: https://codereview.chromium.org/54333009

TBR=johannkoenig@chromium.org


git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232532 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232533 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232532
SVN changes up to revision 232533