How to unset fieldset in hook_form_alter?
The mentioned solution ['#access'] = false will be a possible solution, but if it's not working you may try: 

/**
 * Implements hook_form_FORM_ID_alter().
 */
function YOUR_MODULE_form_FORM_ID_alter(&amp;$form, &amp;$form_state) {

  $form['#after_build'][] = 'YOUR_MODULE_form_FORM_ID_after_build';

}

/**Replace MACHINE_NAME with your fieldset group machine name.**/

function YOUR_MODULE_form_FORM_ID_after_build(&amp;$form, &amp;$form_state) {

  // Hide the B2B group.
  field_group_hide_field_groups($form, array('group_MACHINE_NAME'));

  return $form;
}