[FIX] pos_restaurant: submit order lines only once

This commit reverts [1]. Otherwise, the same order lines may be
submitted several times.

To reproduce the issue:
(Use demo data)
1. Point of Sale > Configuration > Order Printers, edit Kitchen Printer:
    - Printed Product Categories: Food
2. Edit the POS Bar:
    - Enable Order Printer
3. Start a session of POS Bar
4. Select table T1
5. Add a Bacon Burger and submit the order
6. Open another table
7. Reopen table T1
8. Add a Cheese Burger and submit the order

Error: The ticket sent to the kitchen has the bacon burger and the
cheese burger. Only the last one should be sent to the kitchen

When selecting a table, a RPC call gets all information about the
current order. In the server response, the orderlines are sent as new
records:
https://github.com/odoo/odoo/blob/629a4f34ea66f10a981f4b25d5d69281f62853b6/addons/pos_restaurant/models/pos_order.py#L88


Therefore, the orderlines will have a new ID. However, since [1], the
lines identifiers are used to know which lines have changed. This
explains why the bacon burger is sent twice.

[1] 8159e5ac

OPW-2678701

closes odoo/odoo#79418

X-original-commit: 75fb0aa6
Signed-off-by: Masereel Pierre <pim@odoo.com>