Options form subform for exposed filter options.
Overrides FilterPluginBase::buildExposeForm
buildOptionsForm()
public function buildExposeForm(&$form, &$form_state) {
parent::buildExposeForm($form, $form_state);
// @todo There are better ways of excluding required and multiple (object flags)
unset($form['expose']['required']);
unset($form['expose']['multiple']);
unset($form['expose']['remember']);
}