2
In phpmyadmin or another client use this SQL statement:
DELETE FROM <prefix>_bb_posts,<prefix>_bb_posts_text USING <prefix>_bb_posts, <prefix>_bb_posts_text WHERE (<prefix>_bb_posts.uid = 308 AND <prefix>_bb_posts.post_id = <prefix>_bb_posts_text.post_id);
Replace <prefix> with your Xoops DB prefix. I see the spammers uid is 308 from the link you posted. Of course you should backup your database prior to executing this statement.