Delivery Challan are chronological records. There should be no option to delete once a delivery challan no. is processed.
Normally the products issued vide a delivery challan are retunrd back sometimes consumed.

Since material moves outon a delivery challan, the record should always be available.

It is a future reference for movement of goods, Also if a customer decides after returning goods that they now want to finalise the order we will not have records for the same. Like item selected, price etc