/**
* Filter default comment fields
* @param array $fields
*/
function videotube_child_filter_comment_fields( $fields ){
    unset( $fields['email'] );
    $fields['url'] = '</div>';
    return $fields;
}
add_filter( 'comment_form_default_fields', 'videotube_child_filter_comment_fields', 10, 1 );