This removes the need to call `registerAdapter` on
`ZKAPAuthorizerStorageServer`. It looks like that was needed because the
interfaces for it were defined by `implementer_only` which explicitly ignored
interfaces defined by parent classes. Looking at the history, I assume the use
of `implementer_only` was to avoid implementing `RIStorageServer` via
`proxyForInterface`. Given that the later is no longer used, `implementer_only`
is no longer necessary.

We can just have Hypothesis give us a POSIX timestamp and then twiddle our
clock with that value appropriately.  Not much less code but a lot less
explanation.

This is better than stuffing it in later.

Tahoe-LAFS 1.16 changes the way StorageServer determines the current time.
This is great because it gives us a nice place to plug in our fake time.  We
still have to support <1.16 which leaves some not-so-nice stuff around.

If RIStorageServer doesn't define it, don't try to wrap it.

Previously Hypothesis spent a long while putting storage indexes on the
storage servers and creating a list of nodes with non-overlapping storage
indexes and then asserting that, out of no relevant shares, none had expired
leases.

Now all storage servers in the test will have all of the relevant shares and
so all should be visited and updated.

It's better if we don't have to scrape the public key out of the config text,
anyway.