commented location where lookup_sids(), a direct call to the password

commented location where lookup_sids(), a direct call to the password
database API, needs to be replaced with over-the-wire (actually, tcp/ip
loopback) to smbd.

in fact, this is the location where, if we want to put in an nt5 ldap
lookup system or netware NDS instead, we make the calls to resolve
users-to-sids and vice-versa: NOT by replacing rpc_server/srv_samr.c.
(This used to be commit fd886af3317ca806c9c28f71afca5c7b063c1226)