remove links to unsupported documentation

[miabbott]

The Getting Started Guide for setting up an Atomic Cluster and the docs around Kubernetes are old, unmaintained, and hard to provide support for.

Let's stop pointing users at these docs and try to find a better way for users to experiment with kubernetes, etc.

This is not an exhaustive removal of the links to both guides, but the primary entrypoints that I found.

[miabbott]

No idea if this builds or not because middleman is terrible