Revert: Roll libyuv r1708 to r1710 for fix to odd width extract alpha.

Reason for revert: Breaks a WebRTC video test (speculative revert).

Bug: libyuv:798, webrtc:9263
Change-Id: I1edcc8cde1f1ccf74b1b780faac9aace53750099
Reviewed-on: https://chromium-review.googlesource.com/1057087
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: Patrik Höglund <phoglund@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558236}

DEPS

@@ -762,7 +762,7 @@ deps = {
     Var('chromium_git') + '/webm/libwebm.git' + '@' + 'af81f26025b7435fa9a14ad07c58b44cf9280430',
 
   'src/third_party/libyuv':
-    Var('chromium_git') + '/libyuv/libyuv.git' + '@' + 'a7fb978e30398819a350c893f1f93fdd48bd87a6',  # from r1710
+    Var('chromium_git') + '/libyuv/libyuv.git' + '@' + 'a9626b9daf62a9b260737e9c2de821ad087b19a1',  # from r1708
 
   'src/third_party/lighttpd': {
       'url': Var('chromium_git') + '/chromium/deps/lighttpd.git' + '@' + Var('lighttpd_revision'),