NaCl SDK: Move OWNERS file up a directory

All top-level directories should have OWNERS. It looks here like we can just move OWNERS up a directory safely.

Context: https://groups.google.com/a/chromium.org/d/topic/chromium-dev/QVHoLdhhxYk/discussion

BUG=
TBR=bradnelson@chromium.org

Review URL: https://chromiumcodereview.appspot.com/10916057

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@154526 0039d316-1c4b-4281-b951-d872f2087c98