docs: remove kube-dns-autoscaler when upgrading to CoreDNS

[agilgur5]

Summary

Per #6318 (comment) and related comments, the kube-dns-autoscaler is no longer needed when upgrading to CoreDNS.

Details

• there is a separate coredns-autoscaler that is spun up in more recent kOps versions

  • so the kube-dns-autoscaler is no longer needed after an upgrade to CoreDNS - and possibly could conflict if they both targeted the same deployment

• updating the kube-dns-autoscaler was the most confusing part, so this simplifies things a good bit!

• also fix some minor inconsistent spacing in this doc

Misc

Was teaching folks about k8s DNS so came back to the issue to see what the progress was w/ CoreDNS as I had to do this upgrade a couple years ago

[k8s-ci-robot]

Hi @agilgur5. Thanks for your PR.

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[hakman]

Thanks @agilgur5. Should be very useful for those that upgrade clusters.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hakman

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[hakman]

/ok-to-test