moved "rm -f umount" from "remove_checkpoints" to "clean" because if make

is run with parallel jobs the file may not exist yet for remove_checkpoints
to remove

Makefile

@@ -260,10 +260,10 @@ umount:
 
 remove_checkpoints:
 	rm -f mounts compile_options base_system portage sync_portage
-	rm -f umount
 	rm -f parted grub stage3 software preproot sysconfig systools image partitions device-map
 
 clean: umount remove_checkpoints
+	rm -f umount
 	rm -rf loop gentoo
 	rm -rf gentoo
 	rm -rf $(CHROOT)