btrfs: remove SANITY_TESTS check form find_parent_nodes

We define __TRANS_DUMMY always, so this extra ifdef stuff is not needed.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>