If you do not wish to use Discount Coupons ...

Check that you never set up any Discount Coupons ...

Admin ... Gift Certificate/Coupons ... Coupon Admin ...

If any are setup ... click delete to disable them ...

Go to the Admin ... Modules ... Order Totals ... Discount Coupon ... and remove it ...

Now Discount Coupons are not enabled for your shop but can be added at a later date should you wish to use them ...