Solution:1
You can use a custom function hooked in woocommerce_before_checkout_form
action hook that will remove the notice coupon form without disabling coupon functionality in checkout page:
add_action( 'woocommerce_before_checkout_form', 'remove_checkout_coupon_form', 9 );
function remove_checkout_coupon_form(){
remove_action( 'woocommerce_before_checkout_form', 'woocommerce_checkout_coupon_form', 10 );
}
Code goes in function.php file of the active child theme (or active theme).
Tested and works.