sw-order-line-items-grid component causes an error when trying to delete line item from a non-RatePay order

[elena-mb]

In onDeleteItem method, sw-order-line-items-grid component calls this.$super('onConfirmDelete', item, itemIndex), skipping the original onDeleteItem logic of assigning the item.id to this.showDeleteModal. This results in a call to api/order-line-item/false endpoint (instead of calling api/order-line-item/{line-item-id}), which ends in 404.

How to reproduce:

1. Create an order with any payment method other than RatePay
2. Go to admin > order > view the order
3. Try to remove an item from the order by using the actions dropdown