winbind: Simplify query_user_list to only return rids

winbind: Simplify query_user_list to only return rids

Unfortunately this is a pretty large patch, because many functions
implement this API. The alternative would have been to create a new
backend function, add the new one piece by piece and then remove the
original function.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Uri Simchoni <uri@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>