Remove heat.config.sample file

This file keeps breaking our gate, because libraries we depend on
release and the generated content changes.

The check has been disabled, but to avoid the sample config becoming
totally stale, remove it and replace with a README which says
how to generate the current sample config.

Change-Id: I1c43e5cf2a7ab6fa388b91fd420392996c368e72
Merge "Remove heat.config.sample file"