Stop warning users about bug #21018

While working on #14389 (moved) we figured out that when a Tor client connects to an onion service with authorization without the proper authorization client config (or non-existent auth config), Tor will throw out 6 warnings like this:

 [warn] Failed to parse introduction points. Either the service has published a corrupt descriptor or you have provided invalid authorization data, or (maybe!) the server is deliberately serving broken data in an attempt to crash you with bug 21018.

We should consider removing the alarmist warn about bug #21018 (moved) at some point, and maybe that point is now, since it might freak out users for no reason and there is no way for us to learn whether the attack took place.