Remove built-in LDAP Node Terminus

This blurb from the LDAP Node Terminus documentation says it all:

OK: We're very sorry about this, but documentation for how variables work with LDAP has been basically lost to time. The document we inherited from the wiki was very unclear about all this, and we can't budget the time to set up a test environment and confirm it. We don't even know if anyone is using this terminus anymore, to be honest.

The docs practically beg users to switch to use hiera instead. We believe very few users are using this terminus, and we should deprecate it to avoid new users coming across it and feeling our pain.