Kill off another ugly wart from the side of the passdb subsystem.

Kill off another ugly wart from the side of the passdb subsystem.

This time its the pdb_getsampwuid() function - which was only being used by the
SAMR rpc subsystem to gain a 'user session key'.  This 'user session key' is
actually generated at login time, and the other changes here simply move that
data around.

This also means that (when I check some details) we will be able to use the
user session key, even when we are not actually the DC, becouse its one of the
components of the info3 struct returned on logon.

Andrew Bartlett