Hide "Audits" section in Email Preferences when uninstalled

Summary:
`PhabricatorEmailPreferencesSettingsPanel::getAllEditorsWithTags()` queries for all classes extending `PhabricatorApplicationTransactionEditor` and having `getMailTagsMap()` to then pull their editor application class. Thus return the correct editor application class.
Followup to rP821708414e.

`grep -r "('PhabricatorApplicationTransactionEditor'" .` shows only a single result in the Phorge codebase (this `PhutilClassMapQuery->setAncestorClass('PhabricatorApplicationTransactionEditor')` call) so I assume there will be no unwanted side effects.

Closes T16002

Test Plan:
* Uninstall Audit on `/applications/view/PhabricatorAuditApplication/`
* Check for `Audits` section on `/settings/panel/emailpreferences/`
* Re-install Audit and try random actions on a commit like: Accept commit, Raise a concern, Change Project Tags, award token, Subscribe, Unsubscribe, Resign as Auditor, no regressions

Reviewers: O1 Blessed Committers, mainframe98, valerio.bozzolan

Reviewed By: O1 Blessed Committers, mainframe98, valerio.bozzolan

Subscribers: mainframe98, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T16002

Differential Revision: https://we.phorge.it/D25894

src/applications/audit/editor/PhabricatorAuditEditor.php

@@ -22,7 +22,7 @@ final class PhabricatorAuditEditor
   }
 
   public function getEditorApplicationClass() {
-    return PhabricatorDiffusionApplication::class;
+    return PhabricatorAuditApplication::class;
   }
 
   public function getEditorObjectsDescription() {