How can I disable the form confirmation message?
There is no option in Drupal's core that gives you the ability to disable messages but there is a module for that: disable_messages.

Still, I like this approach, which uses drupal_get_messages function implemented in hook_form_alter:

/**
 * Implements hook_form_alter().
 */
function my_module_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  // Define the $form_id for the form which you want to suppress messages for.
  if ($form_id == 'hide_messages_form_id') {
    $form['actions']['submit']['#submit'][] = 'my_module_submit';
  }
}

/**
 * My custom submit handler.
 */
function my_module_submit($form, &amp;$form_state) {
  // Hide drupal 'status' messages. Equally use 'error', 'warning' or 'NULL'.
  drupal_get_messages('status');
  // Or display your own message.
  // drupal_set_message(t('My message.'));
}