Remove all Puppet Dashboard documentation and references

The puppet-dashboard 1.2 documentation confuses and encourages
users to setup puppet-dashboard 1.2. Users should use the 2.0
documentation or a different dashboard product like puppetboard,
foreman or PE Console.

End of puppetlabs support annoncement here:
https://groups.google.com/forum/#!msg/puppet-announce/j44EbTJY7HI/dw1NI9OjWwQJ