Hide "Packages" field in Diffusion Commits query form when application uninstalled

Summary: Fixes T15698

Test Plan:

1. Uninstall Packages via /applications/view/PhabricatorPackagesApplication/
2. Go to /diffusion/commit/, expand the Query form, and see that Packages is not shown anymore

Reviewers: O1 Blessed Committers, 20after4

Reviewed By: O1 Blessed Committers, 20after4

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15698

Differential Revision: https://we.phorge.it/D25506