Don't give weights to v3 dir auths

In the old Torflow, we had a little check that decided not to include opinions about the main network dir auths. That way they remain unmeasured, so they don't attract much network load from clients.

That check doesn't seem to have been done in sbws. So now that we have four bwauths running swbws, moria1 is now getting more traffic that isn't dir auth related: https://metrics.torproject.org/rs.html#details/9695DFC35FFEB861329B9F1AB04C46397020CE31

We could fix this in sbws, to check if the relay has the Authority flag and not write out a line for it.

Or we could fix this on the Tor side (cc @dgoulet), where Tor decides that a bwauth line for an Authority relay should be skipped.