Update calls to DeleteItem to use ActiveItems inline

This highlights how all (except one) call sites duplicate the i argument. With the exception of the use in msg.cpp this can be treated as a offset into activeItems and doesn't care about the real index.

Source/items.cpp

@@ -3567,7 +3567,7 @@ void CornerstoneLoad(Point position)
 		int ii = dItem[position.x][position.y] - 1;
 		for (int i = 0; i < ActiveItemCount; i++) {
 			if (ActiveItems[i] == ii) {
-				DeleteItem(ii, i);
+				DeleteItem(ActiveItems[i], i);
 				break;
 			}
 		}

Source/loadsave.cpp

@@ -928,11 +928,10 @@ void LoadDroppedItemLocations(LoadHelper &file, const std::unordered_map<uint8_t
 void RemoveEmptyLevelItems()
 {
 	for (int i = ActiveItemCount; i > 0; i--) {
-		int ii = ActiveItems[i];
-		auto &item = Items[ii];
+		auto &item = Items[ActiveItems[i]];
 		if (item.isEmpty()) {
 			dItem[item.position.x][item.position.y] = 0;
-			DeleteItem(ii, i);
+			DeleteItem(ActiveItems[i], i);
 		}
 	}
 }