Refactor the pupmod-simp-ganglia module to use data in modules

Refactor the data in the pupmod-simp-ganglia module (https://github.com/simp/pupmod-simp-ganglia) to use the new data-in-modules pattern as per Puppet best practices, as part of the effort to make simp modules more accessible to forge users.
See https://forge.puppet.com/puppetlabs/ntp for an example of data-in-modules.