Remove red coloration from "Logout" menu item

Summary: I made the red stronger (always visible, not just a hover state) for the "Mute" feature, but this made Logout look a little intense. Just make it normal-colored, logging out isn't a big deal.

Test Plan: No longer saw bright red logout action in profile dropdown menu.

Differential Revision: https://secure.phabricator.com/D19044