Drupal 7: How to remove a HTML class from a form item using hook form_alter

content

// remove html class from form item
function theme_name_form_alter(&$form, &$form_state, $form_id) {
  switch ($form_id) {
    case 'form_id':
      $classes = &$form['actions']['item_name']['#attributes']['class'];
      $classes = array_filter($classes , function($e){
        return $e != 'class_to_remove';
      });
    break;
  }   
}

Nice, thanks!