Afform - Drop new/unused setting

This setting was added in a recent merge but hasn't been released.

ext/afform/core/CRM/Afform/Utils.php

-<?php
-/*
- +--------------------------------------------------------------------+
- | Copyright CiviCRM LLC. All rights reserved.                        |
- |                                                                    |
- | This work is published under the GNU AGPLv3 license with some      |
- | permitted exceptions and without any warranty. For full license    |
- | and copyright information, see https://civicrm.org/licensing       |
- +--------------------------------------------------------------------+
- */
-
-use CRM_Afform_ExtensionUtil as E;
-
-/**
- *
- */
-class CRM_Afform_Utils {
-
-  /**
-   * Get a list of authentication options for `afform_mail_auth_token`.
-   *
-   * @return array
-   *   Array (string $machineName => string $label).
-   */
-  public static function getMailAuthOptions(): array {
-    return [
-      'session' => E::ts('Session-level authentication'),
-      'page' => E::ts('Page-level authentication'),
-    ];
-  }
-
-}

ext/afform/core/settings/Afform.setting.php

-<?php
-use CRM_Afform_ExtensionUtil as E;
-
-return [
-  'afform_mail_auth_token' => [
-    'group_name' => 'Afform Preferences',
-    'group' => 'afform',
-    'name' => 'afform_mail_auth_token',
-    'type' => 'String',
-    'html_type' => 'select',
-    'html_attributes' => [
-      'class' => 'crm-select2',
-    ],
-    'pseudoconstant' => [
-      'callback' => 'CRM_Afform_Utils::getMailAuthOptions',
-    ],
-    // Traditional default. Might be nice to change, but need to tend to upgrade process.
-    'default' => 'session',
-    'add' => '4.7',
-    'title' => E::ts('Mail Authentication Tokens'),
-    'is_domain' => 1,
-    'is_contact' => 0,
-    'description' => E::ts('How do authenticated email hyperlinks work?'),
-    'help_text' => NULL,
-    'settings_pages' => ['afform' => ['weight' => 10]],
-  ],
-];