I had a couple communities show up that were purely unsolicited commercial messages for SEO purposes, so I used the following sql queries to thanos snap them out of existence.

delete from community_moderator where community = any( select id from community where name = 'ReplaceMe' );

delete from community_follow where community = any( select id from community where name = 'ReplaceMe' );

delete from notification where reply= any( select id FROM reply WHERE post = ANY( SELECT id FROM post WHERE community= any( select id from community where name = 'ReplaceMe' ) ));

DELETE FROM reply WHERE post = ANY( SELECT id FROM post WHERE community= any( select id from community where name = 'ReplaceMe' ) );

DELETE FROM notification WHERE parent_post = ANY( SELECT id FROM post WHERE community= any( select id from community where name = 'ReplaceMe' ) );

delete from community where name = 'ReplaceMe';