Rip back out puppet-module-data

Well, it was a nice idea in https://github.com/jfryman/puppet-nginx/pull/453, but there have been several reported issues with the update.

1) Performance hits. This is a bit anecdotal... I've asked for data but have not received any yet. Nonetheless, I have heard from a few folks that introducing `puppet-module-data` adds extra time to catalog compilation.
2) Installation difficulty. I field quite a bit of out of band support requests associated with `puppet-module-data`. It has proven to be hacky enough to cause errors in several edge cases. Because it is not part of Puppet Core, it increases the barrier to entry for a fair number of folks.

I love this pattern, but it need a lot of love, and until it becomes a first class citizen, it needs to be ripped out before we hit 1.0. So, while I hate making a big change and then ripping it out... it's better to do now than before it becomes too unwieldy. 
Should be `$conf_dir = $_conf_dir`