make the actiona_compute only run once when generating MO through procurement order

I assume that the reason to call `action_compute` method in `procurement.make_mo` is to pass in the `properties` parameters , and thus the BOM of the generated MO will be selected according to the BOM Properties on the related procurement order. 
However, the action_compute will be called the second time by the workflow when the MO is confirmed. The double call of the `action_compute` method caused performance issue and  those unnecessary unlink product_lines process.
This fix take care of the bom properties match inside action_compute, and thus remove the needs to call `action_compute` in `procurement.make_mo`.