Remove “optional” text from WooCommerce checkout fields

Optional input fields in WooCommerce checkout is marked with (optional) text. This text can be removed without editing any WooCommerce template, by using woocommerce_form_field filter.

function careless_remove_checkout_optional_text( $field, $key, $args, $value ) {
    if( is_checkout() && ! is_wc_endpoint_url() ) {
        $optional = '&nbsp;<span class="optional">(' . esc_html__( 'optional', 'woocommerce' ) . ')</span>';
        $field = str_replace( $optional, '', $field );
    }
    return $field;
}
add_filter( 'woocommerce_form_field' , 'careless_remove_checkout_optional_text', 10, 4 );

Code goes in the functions.php file of your active theme.