Removes the Discount Code field from the checkout form.
<?php
/*
 * Plugin Name: Easy Digital Downloads - Remove Discount Field
 * Description: Removes the Discount Code field from the checkout form.
 * Author: Easy Digital Downloads
 * Author URI: https://easydigitaldownloads.com/
 * Version: 1.0
 */

function pw_edd_remove_discount_field() {
	remove_action( 'edd_checkout_form_top', 'edd_discount_field', -1 );
}
add_action( 'init', 'pw_edd_remove_discount_field' );
To implement this snippet on your site, create a brand new, empty WordPress plugin and paste the above code inside.