Use new mount args (mount "ufs" instead of MOUNT_UFS).

vnconfig doesn't seem to be in Lite2, although dev/vn is.  The Lite2
merge in userland has converted all mount calls except this one and
one for devfs in init, so we can drop support for old mount args soon.

Vnconfig probably shouldn't support mounting - it only supports ufs.

usr.sbin/vnconfig/vnconfig.c

@@ -314,7 +314,7 @@ config(vnp)
 
 			args.fspec = dev;
 			mflags = (flags & VN_MOUNTRO) ? MNT_RDONLY : 0;
-			rv = mount(MOUNT_UFS, oarg, mflags, &args);
+			rv = mount("ufs", oarg, mflags, &args);
 			if (rv)
 				perror("mount");
 			else if (verbose)