further improve NPC sitting

try more forcefully to remove the arrow.

src/main/java/net/aufdemrand/denizen/npc/traits/SittingTrait.java

@@ -79,6 +79,7 @@ private void standInternal() {
         Entity vehicle = npc.getEntity().getVehicle();
         npc.despawn();
         npc.spawn(npc.getStoredLocation().clone().add(0, 0.5, 0));
+        vehicle.setPassenger(null);
         if (vehicle != null && vehicle.isValid()) {
             vehicle.remove();
         }