LJ::delete_all_comments — deletes all comments from a post, permanently, for when a post is deleted
LJ::delete_all_comments(u, nodetype, nodeid
u. A hashref of a row from the user table, sometimes called a "user object". Although only initially a row from the user table, gets a lot of tacked onto it from various other LJ API functions.
nodetype. The thread nodetype (probably 'L' for log items).
nodeid. The thread nodeid for the given nodetype (probably the jitemid from the log2 row).