vfs: remove stale comment in inode_operations

The big warning comment that is currently at the end of struct
inode_operations was added as part of this commit:

4aa7c634 ("vfs: add i_op->dentry_open()")

It was added to warn people not to use the newly added 'dentry_open'
function pointer.

This function pointer was removed as part of this commit:

4bacc9c9 ("overlayfs: Make f_path always point to the overlay and
		f_inode to the underlay")

The comment was left behind and now refers to nothing, so remove it.
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/fs.h

@@ -1665,8 +1665,6 @@ struct inode_operations {
 			   umode_t create_mode, int *opened);
 	int (*tmpfile) (struct inode *, struct dentry *, umode_t);
 	int (*set_acl)(struct inode *, struct posix_acl *, int);
-
-	/* WARNING: probably going away soon, do not use! */
 } ____cacheline_aligned;
 
 ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,