Scuttle Workboards if Maniphest is not installed

Summary: fix T9718.

Test Plan: view project page when maniphest is and isn't. Look for Workboards.

Reviewers: #blessed_reviewers, chad

Reviewed By: #blessed_reviewers, chad

Subscribers: epriestley

Maniphest Tasks: T9718

Differential Revision: https://secure.phabricator.com/D14438