btrfs: remove stale comments about fs_mutex

The fs_mutex has been killed in 2008, a213501153fd66e2 ("Btrfs: Replace
the big fs_mutex with a collection of other locks"), still remembered in
some comments.

We don't have any extra needs for locking in the ACL handlers.

Signed-off-by: David Sterba <dsterba@suse.com>
1 file changed