convert xenfs

entirely static tree, populated by simple_fill_super(). Can switch
to kill_anon_super() without any other changes.

Signed-off-by: Al Viro <[e-mail]>

drivers/xen/xenfs/super.c

···
 	.owner =	THIS_MODULE,
 	.name =		"xenfs",
 	.init_fs_context = xenfs_init_fs_context,
-	.kill_sb =	kill_litter_super,
+	.kill_sb =	kill_anon_super,
 };
 MODULE_ALIAS_FS("xenfs");