btrfs: Remove redundant btrfs_release_path from btrfs_unlink_subvol

btrfs: Remove redundant btrfs_release_path from btrfs_unlink_subvol

commit 5b7d687ad5913a56b6a8788435d7a53990b4176d upstream.

Although it is safe to call this on already released paths with no locks
held or extent buffers, removing the redundant btrfs_release_path is
reasonable.

Signed-off-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[bwh: Backported to 3.16 as dependency of commit d49d3287e74f
 "btrfs: fix invalid removal of root ref"]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>