[FIX] product: removal of hardcoded value in product template

Steps to reproduce:
- install sales
- activate units of measures and variants
- set imperial units under general settings (pounds for weight and ft³ for volume)
- create at least 2 variants on a product and access them via the smart button
from product.template

Previous behavior:
the volume remains in m³, it is hardcoded in the template

Current behavior:
the volume is printed just like the weight (generic uom notation)

opw-2186965

closes odoo/odoo#44649

Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>