Debian: Use dh_installsystemd to fix enabling/restarting on install/update

As a side effect the unit files now live in "/lib/systemd/system" instead of
"/usr/lib/systemd/system".

debian/install

 uffd-ldapd /usr/sbin/
-debian/contrib/uffd-ldapd.service /usr/lib/systemd/system/
-debian/contrib/uffd-ldapd.socket /usr/lib/systemd/system/
-debian/contrib/uffd-ldapd.conf /etc/
+debian/uffd-ldapd.conf /etc/