linux_aura: Disable TwoClientThemesSyncTest.

Casualty of turning on linux_aura.

BUG=304554
TBR=tim@chromium.org

Review URL: https://codereview.chromium.org/26157002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227211 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227211