Delete orphaned deploy tokens

What does this MR do and why?

After !160526 (merged) records are no longer left orphaned when a project or group is deleted.

This merge request uses a batched background migration to delete all records that were left in this orphaned state before the fix was implemented. We need to remove these records to be able to add a NOT NULL constraint on project_id/group_id, which is required for it to be used as the sharding key(s).

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Related to #474370