kernfs: remove the unused lockdep_key field in struct kernfs_ops

Not actually used anywhere.
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210913054121.616001-4-hch@lst.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/kernfs.h

@@ -269,10 +269,6 @@ struct kernfs_ops {
 			 struct poll_table_struct *pt);
 
 	int (*mmap)(struct kernfs_open_file *of, struct vm_area_struct *vma);
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-	struct lock_class_key	lockdep_key;
-#endif
 };
 
 /*