Drop support for older versions of the hidden service protocol
We've supported v3 introduce{1,2} cells since 0.2.1.
We've supported v2 descriptors since 0.2.0.
There is no need for clients and servers to continue supporting older versions of the hidden service protocols; there is probably no need for "hidden service authorities" to exist; and there is probably a bunch of other code here we can discard too.
The one wrinkle to think about is that removing support here might enable an adversary to tell when a client or service has switched to a newer version of Tor. Generally, we don't care about that, but we should still think about it.