Remove undocumented puppetversion key functionality in module metadata

The [validate_puppet_version](https://github.com/puppetlabs/puppet/blob/04a60fbff5dbc0d2a5818c671cecc20032b0fae7/lib/puppet/module.rb#L286) method in the Puppet::Module class will look for `puppetversion` in a module's metadata. It will compare that string (cannot specify array or range) against the running Puppet version and fail to install the module if the running version and the expressed puppetversion don't match.

We'll need to remove this functionality.

This ticket is the public reference to this behavior.

EDIT: We left the accessor and functions associated so as not to make a breaking change. This is only making the check never fail for now.