Contact form 7 remoce select box (Dropdown) default value

function my_wpcf7_form_elements($html) {
function replace_include_blank($name, $text, &$html) {
$matches = false;
preg_match('/]*>(.*)<\/select>/iU', $html, $matches);
if ($matches) {
$select = str_replace('---', '' . $text . '', $matches[0]);
$html = preg_replace('/]*>(.*)<\/select>/iU', $select, $html);
}
}
replace_include_blank('mc4wp-age', 'AGE*', $html);
return $html;
}
add_filter('wpcf7_form_elements', 'my_wpcf7_form_elements');