Support strict_variables by removing dynamic lookups

This pull request removes a bunch of existing functionality.  I would understand if you don't want to merge it.

My organization would like to enable strict_variables for our Puppet compilation.  The current design of this module is not compatible with strict_variables, because it uses dynamic lookups to test for parameters.  Dynamic lookups are [deprecated](https://docs.puppetlabs.com/guides/scope_and_puppet.html).

With that in mind, I propose to remove these lookups entirely in favor of class parameters.