drupal 8 - change button and remove preview on form

In my mytheme.theme file I put the following code and I could both remove the preview button and also change the submit button text.

function mytheme_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {

  if (in_array($form_id, ['contact_message_feedback_form', ])) {
    $key = ($form_id == 'contact_message_feedback_form') ? 'actions' : 'basic';
    $form[$key]['submit']['#value'] = 'My Submit Message';
    $form[$key]['preview']['#access'] = FALSE;
  }
}