wc-hide-coupons-cart-checkout.php

<?php

// hide coupon field on cart page
function hide_coupon_field_on_cart( $enabled ) {

	if ( is_cart() ) {
		$enabled = false;
	}

	return $enabled;
}
add_filter( 'woocommerce_coupons_enabled', 'hide_coupon_field_on_cart' );

// hide coupon field on checkout page
function hide_coupon_field_on_checkout( $enabled ) {

	if ( is_checkout() ) {
		$enabled = false;
	}

	return $enabled;
}
add_filter( 'woocommerce_coupons_enabled', 'hide_coupon_field_on_checkout' );