[FIX] product: weight unit
[FIX] product: weight unit

Since commit 52a85e57b9a6353c14abdb, it is possible to configure the
weight unit. Therefore, we should not hardcode `kg` anymore.

opw-1919821

closes odoo/odoo#30147
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo