samba-tool ntacl: remove unused imports and variables

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Noel Power <noel.power@suse.com>

Autobuild-User(master): Douglas Bagnall <dbagnall@samba.org>
Autobuild-Date(master): Thu Nov  1 09:40:02 CET 2018 on sn-devel-144
