Remove some skip lines for webgl tests.

The webgl directory no longer exists and the other tests pass
according to the trybots.

TBR=kbr@chromium.org

Review URL: https://chromiumcodereview.appspot.com/21385003

git-svn-id: svn://svn.chromium.org/blink/trunk@155268 bbb929c8-8fbe-4397-9dbb-9b2b20218538