Remove heat-cli-guide

The heat command line clients are documented now better in the
OpenStack End User Guide:

http://docs.openstack.org/user-guide/content/heat-stack-create.html
http://docs.openstack.org/user-guide/content/heat_client_commands.html

The content here is thus not needed anymore, as the README.rst says:
"This documentation should eventually end up in the OpenStack
documentation repositories `api-site` and `openstack-manuals`."

Change-Id: I297252d7f8eee383ce6252a5db44111630fbe29b
Merge "Remove heat-cli-guide"