main/unbound: remove dependency on dns-root-hints
The dns-root-hints dependency has been introduced in . Strictly speaking dns-root-hints is not necessary as unbound provides builtin root hints. This change switches to using the builtin root hints by default, thereby avoiding installation of a cron and a dependency on gnupg. If desired, users can still manually install and configure dns-root-hints with unbound.
See #11324 for further information on this topic.