[FIX] stock: prevent serial number deletion on stock.move

prodlot_id field may be required due to constraint `_check_tracking`.
When a stock.production.lot is deleted, the constraint on linked stock.move is
not checked. To avoid inconsistency, restrict the suppression.
To allow the modification of existing stock.move, remove the states attribute on
the field definition.

As removal of serial may impact the traceability, it makes sense on buisness
point of view to force the modification of previous stock.move, even if the
constraint would not have been violated.
The list of linked stock.move is present on the serial form view making
the operation easier.

Fixes #3560, lp:1176912