Validate that there are no more cross join allowances in the codebase that would negatively affect decomposition

Part of the sec-decomposition process has been to use the allow_cross_joins_across_databases helper to suppress database warnings relating to queries that should not be permitted according to the gitlab_schema configurations in the respective tables yaml files.

We need to ensure that these have all be removed before we attempt to proceed with decomposition. Ideally they should all be covered by a corresponding issue, but this issue exists as a reminder to do a final safety validation and ensure none have escaped our notice.