Added users-delete API endpoint

- Refactored some delete checks into repo.
- Added tests to cover.
- Moved some translations to align with activity/logging system.

resources/lang/en/activities.php

@@ -59,6 +59,9 @@ return [
     'webhook_delete' => 'deleted webhook',
     'webhook_delete_notification' => 'Webhook successfully deleted',
 
+    // Users
+    'user_delete_notification' => 'User successfully removed',
+
     // Other
     'commented_on'                => 'commented on',
     'permissions_update'          => 'updated permissions',