[FIX] point_of_sale: remove 0€ payment line of orders

Current behavior:
When an order contains a payment line with 0€, and a customer account
payment line. Then you close the PoS and invoice the order from an other
PoS session, you get an error.

Steps to reproduce:
- Open PoS, make a new order with a payment line of 0€ and a customer
  account payment line.
- Close the session and open a new one.
- Go in the paid order, and try to invoice it.
- You get an error.

Fix:
To fix the issue we just remove the useless 0€ payment line.

opw-3477486

closes odoo/odoo#134702

Signed-off-by: Joseph Caburnay (jcb) <jcb@odoo.com>