function klassik_de_html_head_alter(&$head_elements) {
  unset($head_elements['system_meta_generator']);
  foreach ($head_elements as $key => $element) {
    if (isset($element['#attributes']['rel']) && $element['#attributes']['rel'] == 'canonical') {
      if ( drupal_is_front_page() ) {
        unset($head_elements[$key]);
      }
    }
  }
}