add_filter( 'woocommerce_cart_shipping_method_full_label', 'remove_local_pickup_free_label', 10, 2 );
function remove_local_pickup_free_label($full_label, $method){
$full_label = str_replace("(Gratuit)","",$full_label);
return $full_label;
}
Source: https://wordpress.org/support/topic/remove-free-word-in-shipping-method-label