aura: Disable clipboard tests until aura has clipboard support.

BUG=97845
TEST=gfx_unittests

Review URL: http://codereview.chromium.org/8342050

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@106413 0039d316-1c4b-4281-b951-d872f2087c98