Test performance improvement between current query:

self.where("id not in (?) OR (schema2_id IS NULL AND schema1_id IS NULL)", Katello::RepositoryDockerMetaTag.pluck(:docker_meta_tag_id) + [0]).delete_all

vs 

self.where("(id != 0 and id not in (select docker_meta_tag_id from #{Katello::RepositoryDockerMetaTag.table_name})) OR (schema2_id IS NULL AND schema1_id IS NULL) ").delete_all

Also, have this method called once per CV version delete vs once per CV version repo delete to save unnecessary calls.