Customized Comment Form Issues

You can unset this field like that :

function wpse_109744_comment_form_fields($fields) {
 if(isset($fields['url']))
  unset($fields['url']);
}
$fields ['email'] = 'your markup';
$fields ['author'] = 'your markup';

$return $fields;
add_filter('comment_form_default_fields', 'wpse_109744_comment_form_fields')

EDIT :