(maint) Remove templatedir from Debian packaging

The `templatedir` setting has been deprecated since Puppet 3.6.2 and isn't even
set in RedHat packages. Remove this setting from the `puppet.conf` used by
Debian packaging scripts.
The default is `$vardir/templates`.  However, IIRC, the `templatedir` may be a relic from a time before modules contained templates.

However, the setting is marked as "completely" deprecated and so will be disappearing in Puppet 4 anyway. The 3.7 [deprecation docs](https://docs.puppetlabs.com/puppet/3.7/reference/deprecated_settings.html#templatedir) state:

> Now
>
> When given a relative path, the template function will try to find templates in this directory before trying to find them in modules.
>
> In Puppet 4.0
>
> The template function will only search modules when given a relative path.

Maybe we should roll this into the change that removes `templatedir` from 4.0 --- I was just responding to the annoyance of deprecation warnings from a clean `apt-get install puppet` from the packages on apt.puppetlabs.com.

In general, the default configs in `ext/debian/pupept.conf` and `ext/redhat/puppet.conf` are _significantly_ different. We may want to look into converging them as part of Puppet 4.