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 <viro@zeniv.linux.org.uk>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -6045,11 +6045,6 @@ static int btrfs_dentry_delete(const struct dentry *dentry)
 	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)
 {
@@ -10844,5 +10839,4 @@ static const struct inode_operations btrfs_symlink_inode_operations = {
 
 const struct dentry_operations btrfs_dentry_operations = {
 	.d_delete	= btrfs_dentry_delete,
-	.d_release	= btrfs_dentry_release,
 };