Remove WooCommerce "Place Order" button

function.php (or Additional CSS)

add_filter('woocommerce_order_button_html', 'remove_order_button_html' );
function remove_order_button_html( $button ) {
 class

    foreach( WC()->cart->get_cart() as $cart_item ) {
        if( $cart_item['data']-> {
            $found = true; 
            break; // We stop the loop
        }
    }
    if( $found )
        $button = '';

    return $button;
}