[FIX] mrp: double consuming in backorder operations

- Create product FP product to manufacture
- Create BoM:
  - 10 units of FP
  - Product CP (component)
  - two operations.
- Create MO for FP and plan.
- Complete operation 1 for the 10 units
- Complete operation 2 for 4 units only
- Mark MO as done for 4 units
- Click Create Backorder
- Check backorder MO

Operation 1 is present, marked todo for 6 units,
but it was completed for all 10 units.

With this commit the quantity todo for the corresponding operation in
the backorder is updated to match the qty already produced

Removing `qty_producing` as it is computed according to
https://github.com/odoo/odoo/blob/ff648a0ace9cf72274211662707e7ee33fc73252/addons/mrp/models/mrp_workorder.py#L50



opw-2374640

closes odoo/odoo#61603

Signed-off-by: agr-odoo <agr-odoo@users.noreply.github.com>