[REVERT] account: unbalanced entry with price_unit 0

This fix will try to write a new amount value on the tax when an
invoice is created from POS, that will raise a user error preventing the
creation of the order.

This reverts commit bd621fd4.

OPW-2855694

closes odoo/odoo#91658

Signed-off-by: Masereel Pierre <pim@odoo.com>