Check is viewer is a participant before showing count

Summary: In Conpherence ProfileMenuItem we show an unread count if you're a participant, but all message count if you're not. Just remove that.

Test Plan: Log out of room in Conpherence, leave messages on second account, check menu item on both accounts.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17664