Revert 264433 "Roll libvpx 263116:264320"

This is a speculative revert of a libvpx roll to unblock dev release.

BUG=366025

> Roll libvpx 263116:264320
> 
> Enable AVX2 code:
> https://codereview.chromium.org/236183003
> 
> Fix Win build issues:
> https://codereview.chromium.org/239003004
> 
> Leave AVX2 ready but off:
> https://codereview.chromium.org/240153006
> 
> Remove all the AVX2 references:
> https://codereview.chromium.org/240113008
> 
> Review URL: https://codereview.chromium.org/236263002

TBR=johannkoenig@google.com

Review URL: https://codereview.chromium.org/252003003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266500 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -35,7 +35,7 @@ vars = {
   "google_toolbox_for_mac_revision": "662",
   "libaddressinput_revision": "176",
   "libphonenumber_revision": "621",
-  "libvpx_revision": "264320",
+  "libvpx_revision": "263116",
   "lss_revision": "26",
 
   # These two FFmpeg variables must be updated together.  One is used for SVN