This was a very straightforward to remove dependency -- errors largely
don't need as much typing as APIs, for instance, due to their tendency
to be handled by a simple print.

And if there's interest, the user of this can convert the Account ID
back to a strongly typed type.

Now there'll be fewer concerns about changing the protocol with
accidental changes to the runtime, and most importantly we have a place
where we can develop the runtime's API (cf limited replayability) and
the protocol independently.

Since the external-facing parts of these errors are now in
near-primitives, it is up to that crate to also generate the relevant
schemas.