The purpose of this commit is to simplify the `mrp.production` model in
reducing the number of date field.
The following fields was kept:
- `date_planned_start`: the planned date for the beginning of the MO
- `date_planned_finished`: the planned date for the ending of the MO
- `date_start_wo`: the preferred date to start a Work Order in case
the MO will plan one.
- `date_deadline`: is only indicative and is automatically set when
the manufacturing order is needed for a sale order.
- `date_start` and `date_finished`: no changes.
Task #1935229
Co-authored-by: Whenrow <whe@odoo.com>
