nspawn: skip machine registration

No need to do this since we don't run an init system in the build root.

arch-nspawn.in

@@ -94,11 +94,8 @@ copy_hostconf
 
 eval $(grep '^CARCH=' "$working_dir/etc/makepkg.conf")
 
-machine_name="${working_dir//[![:alnum:]_-]/-}"
-machine_name="${machine_name#-}"
-
 exec ${CARCH:+setarch "$CARCH"} systemd-nspawn 2>/dev/null \
 	-D "$working_dir" \
-	--machine "$machine_name" \
+	--register=no \
 	"${mount_args[@]}" \
 	"$@"