Cleanup inventory records when an order is Deleted

*Overview: *
Leaving item records in inventory that were never received which reference an order that has been deleted prevents the user from maintaining a clean and relevant inventory.

Note: We need to discuss with the inventory team what they would like us to do with instance/holding/item records that acquisitions might have created if the order is deleted. – Leave inventory records, just delete holdings/items

Given an order was created and opened
When one or more items are in the item status "On order" and the order is deleted
Check if the item doesn't have any requests associated with it
Then those piece records and item records are deleted if both the above conditions are satisfied. Leave the Items in any other status as-is

Given the On order item records are deleted in the above step
When the holding no longer has items related to it
Check that no Order lines have locations that match that holding **
If none match
Then delete the holding

Acceptance criteria:

• pieces, items and holdings are deleted according to the logic described above
• Unit tests are updated
• API tests are updated

Notes:

• • If so, we need to track that mod-orders created the record... either in the order/po_line or the holding record.
  • Must be careful not to remove if other po_lines are using those records.