btrfs: take the last remnants of ->d_fsdata use out

[spotted while going through ->d_fsdata handling around d_splice_alias();
don't really care which tree that goes through]

The only thing even looking at ->d_fsdata in there (since 2012)
had been kfree(dentry->d_fsdata) in btrfs_dentry_delete(). Which,
incidentally, is all btrfs_dentry_delete() does.

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

fs/btrfs/inode.c

···
 	return 0;
 }
 
-static void btrfs_dentry_release(struct dentry *dentry)
-{
-	kfree(dentry->d_fsdata);
-}
-
 static struct dentry *btrfs_lookup(struct inode *dir, struct dentry *dentry,
 				   unsigned int flags)
 {
···
 
 const struct dentry_operations btrfs_dentry_operations = {
 	.d_delete	= btrfs_dentry_delete,
-	.d_release	= btrfs_dentry_release,
 };