main/unbound: remove dependency on dns-root-hints

The dns-root-hints dependency has been introduced in [1]. 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.

[1]: https://github.com/alpinelinux/aports/pull/5950
Status Job ID Name Coverage
  Lint
failed #82498
x86_64 docker-alpine allowed to fail
lint

00:00:33

 
  Build
passed #82503
aarch64 ci-build docker-alpine
build-aarch64

00:01:18

passed #82504
armv7 ci-build docker-alpine
build-armv7

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passed #82502
ppc64le ci-build docker-alpine
build-ppc64le

00:01:28

passed #82638
docker-alpine ci-build s390x
build-s390x

00:00:57

passed #82500
x86 ci-build docker-alpine
build-x86

00:01:08

passed #82499
x86_64 ci-build docker-alpine
build-x86_64

00:00:58

failed #82501
s390x ci-build docker-alpine
build-s390x

 
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