Migrate users off of torrc templates

Via discussion

Can we kill off this sentence, and its use in client-only-v6.tmpl, in a seubsequent branch?

Tor 0.2.9 is long gone...

Removed the comment.

For the moment I left in the behavior of client-only-v6.tmpl disabling them. It seems confusing to change it since there's also client-only-v6-md.tmpl and that's the only difference.

We could do some kind of careful migration here, but I think it's not worth bothering with vs migrating network scripts and users to not use templates at all.

i.e. I think what we actually want to do is migrate users off of setting torrc at all, but if not there's some cleanup that could be done to the remaining compatibility layer.