[FIX] purchase: use field in purchase_stock

The field move_dest_ids is now defined in purchase_stock (since the split at
rev 8d4609a1db)

The line was added in purchase at f6b3247c31 in 11.0 but incorrectly forward
ported.

This commit only moves the code to the appropriate module.

addons/purchase/models/purchase.py

@@ -324,7 +324,6 @@ class PurchaseOrder(models.Model):
             for inv in order.invoice_ids:
                 if inv and inv.state not in ('cancel', 'draft'):
                     raise UserError(_("Unable to cancel this purchase order. You must first cancel the related vendor bills."))
-            order.order_line.write({'move_dest_ids':[(5,0,0)]})
 
         self.write({'state': 'cancel'})
 

addons/purchase_stock/models/purchase.py

@@ -105,6 +105,9 @@ class PurchaseOrder(models.Model):
 
             for pick in order.picking_ids.filtered(lambda r: r.state != 'cancel'):
                 pick.action_cancel()
+
+            order.order_line.write({'move_dest_ids':[(5,0,0)]})
+
         return super(PurchaseOrder, self).button_cancel()
 
     @api.multi