R1:67a5dfa662a8

Notifications - hide header dropdown if app is uninstalled

Summary: Fixes T5019.

Test Plan: uninstalled notifications and dropdown disappeared too

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5019

Differential Revision: https://secure.phabricator.com/D9121