s4-auth Rework auth subsystem to remove struct auth_serversupplied_info

s4-auth Rework auth subsystem to remove struct auth_serversupplied_info

This changes auth_serversupplied_info into the IDL-defined struct
auth_user_info_dc.  This then in turn contains a struct
auth_user_info, which is the only part of the structure that is
mainted into the struct session_info.

The idea here is to avoid keeping the incomplete results of the
authentication (such as session keys, lists of SID memberships etc) in
a namespace where it may be confused for the finalised results.

Andrew Barltett