[UF5] AppController says "safe to be deleted", but this breaks 4 routes

[StrykeSlammerII]

AppController class in the skeleton says it is "safe to be deleted", but doing so causes errors similar to Fatal error: Uncaught RuntimeException: Named route does not exist for name: index in /home/strike/Frosting/UF5-native/vendor/slim/slim/Slim/Routing/RouteCollector.php
chat link: https://chat.userfrosting.com/channel/support?msg=pCkTbS8m33m64qSjH

/, /legal, /about, and /privacy are the affected routes.

Most full sites will want to provide their own pages here, but dependent sprinkles should be able to use the defaults without including or overriding AppController.

[lcharette]

To fix, it should be documented in the skeleton that while these Controllers are safe to be deleted, there's also another step to delete the route.

Plus, index name route should not be required / hardcoded in the navigation template (or provide a fallback), so an exception is not thrown if the index route doesn't exist (or at least, a 404 page is thrown instead)

[lcharette]

Done for part one :)