prop224: Onion service rev counters are useless and actually harmful for scalability

Armadev discovered that hsv3 revision counters are harmful to scalability since if an onion service is hosted by multiple servers (like the fb one), every server should have visibility of the revision counter if they want to publish a descriptor.

We should figure out whether there is an easy way around that, or whether this is actually a big problem for scalable v3s. We should also consider how this works out with onionbalance-based designs.

Rev counters are there so that HSDirs (and other actors) cannot replay old HS descriptors. However, they are not really needed since now HS descriptors are only replayable for a day (before the blinded key gets refreshed), and also HSDirs could keep a replay cache of the descriptor assigned to a blinded key.

If we decide to rip them off, the way to do it is in two painful steps: a) Remove rev counter checking from HSDirs, and do a replay cache or something. b) In the far future, when all HSDirs have upgraded to (a), rip out the rev counter code from onion services.