API Move some code to framework to be reusable

Some of this code needs to be usable on classes other than SiteTree with
the CMSMain refactoring.

code/Model/RedirectorPage.php

@@ -21,12 +21,7 @@
  */
 class RedirectorPage extends Page
 {
-    /**
-     * @deprecated 5.4.0 use class_description instead.
-     */
-    private static $description = 'Redirects requests to another location';
-
-    private static string $class_description = 'Redirects requests to another location';
+    private static $class_description = 'Redirects requests to another location';
 
     private static $icon_class = 'font-icon-p-redirect';