Remove unnecessary test to determine if the order should be voided

* The logic can be simplified so that if the payment total is zero
  (which indicates no payments, a capture + refund, or a void) the order
  payment_state should be set to void.
Merge pull request #43 from MountainRoseHerbs/2-3-stable-mrh-fix-order-cancellation

Fix order cancellation to set the order payment_state to void