cups.inc: remove template service from SYSTEMD_SERVICE

this template service need to triggered by org.cups.cups-lpd.socket,
which will assigned an instance id for org.cups.cups-lpd@.service,
like org.cups.cups-lpd@0.service. add this in SYSTEMD_SERVICE will
cause post scriptlet fail as:
Failed to start org.cups.cups-lpd@.service: Unit name org.cups.cups-lpd@.service is missing the instance name.
See system logs and 'systemctl status org.cups.cups-lpd@.service' for details.

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>