Re-add shuffling for LFK cleanup

This change restores the table shuffling to ensure even processing of
deleted records.

app/services/loose_foreign_keys/process_deleted_records_service.rb

@@ -52,7 +52,7 @@ module LooseForeignKeys
     end
 
     def tracked_tables
-      @tracked_tables ||= Gitlab::Database::LooseForeignKeys.definitions_by_table.keys
+      @tracked_tables ||= Gitlab::Database::LooseForeignKeys.definitions_by_table.keys.shuffle
     end
   end
 end