Don't display Standard post format twice in the meta box if the theme unnecessarily mentions it in the add_theme_support() call.

props ptahdunbar, nacin, pushplaybang, obenland.
fixes #16555.

git-svn-id: https://develop.svn.wordpress.org/trunk@30038 602fd350-edb4-49c9-b593-d223f7449a82