Hide uninstalled applications on the "Home Application Tiles" preferences page

Summary: Fixes T4685.

Test Plan: loaded home page settings and saw phrequent, uninstalled phrequent, refreshed, and no longer saw phrequent!

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T4685

Differential Revision: https://secure.phabricator.com/D8640