I did it myself,
woocommerce/templates/checkout/form-coupon.php
just add this line
if ( $woocommerce->checkout)
return;
This section and others are being generated from the woocommerce-hooks.php file in the plugin directory. Another way to remove this functionality from the checkout page would be to de-register the action hook being used to generate the content.
You would simply need to place the following code at the top of the form-checkout.php page (just under global $woocommerce to remove the coupon form call:
remove_action( 'woocommerce_before_checkout_form', 'woocommerce_checkout_login_form', 10 );
That should do the trick!
The above post removes the login form, not the coupon form – to do this, insert the following code in your theme’s functions.php file:
remove_action( 'woocommerce_before_checkout_form', 'woocommerce_checkout_coupon_form', 10 );
There is an easy way to turn off Coupons from within WooCommerce
Dashboard
> WooCommerce
> Settings
> General
> Coupons
> Enable the use of Coupons (uncheck this)
Cheers
