Get rid of url in WP twentyten theme

In wordpress the default theme in v3.0 is twentyten. I'm trying to remove the url box from the comments form. Looking in comments.php there seems to be 开发者_JAVA百科no reference to it, as has been in past versions.

How do I remove the url box from comments in this theme?

For the functions.php:

add_filter('comment_form_default_fields', 'filter_strip_url');

function filter_strip_url($fields)
{
    unset($fields['url']);
    return $fields;
}