POS Remove restriction on change quantity

The French Point of Sale certification module (l10n_fr_pos_cert) normally blocks cashiers from reducing the quantity of a product on a POS order line or removing a line once it has been added. This module disables that protection.

• It works by overriding the Point of Sale behaviour that decides whether line quantity changes are forbidden, making it always allow changes.
• The change is applied only in the Point of Sale interface; no new menus, screens, buttons or reports are added.
• It does not create or modify any database model, and it does not add any new business rules, checks, emails or scheduled jobs.
• It simply loads an extra script into the Point of Sale assets, alongside the existing French certification scripts.

Because the restriction is removed, cashiers can lower quantities or delete lines in the POS as they could before the French certification rules were applied. This module depends on l10n_fr_pos_cert and is intended for French companies that need to bypass this specific control while keeping the rest of the certification module installed.