LJ::leave_community — Makes a user leave a community. Takes care of all reluser and friend stuff.
LJ::leave_community(uuserid, ucommid, defriend);
uuserid. a userid or u object of the user doing the leaving
ucommid. a userid or u object of the community being left
defriend. remove comm from user's friends list
1 if success, undef if error of some sort (ucommid not a comm, uuserid not in