Clean domain files

There seems to be several domain files in some cases, and many look like noise.

For example, let's take `first-responders`:

- `domain.pddl`: seems to be original with lots of dummy non-used `:requirements`, like conditional effects
- `domain-fixed.pddl`: same as `domain.pddl` but with just the used requirements, namely, `:typing :negative-preconditions :non-deterministic`
- `domain-fixed.pddl.fip`: this seems to be the determinization that FIP used, it has lots of deterministic action versions, different signature of actions. I don't think it is good to keep planning specific encodings like this one.

I propose we try to aim for just one `domain.pddl` unless there is a good reason to keep multiple versions.

In this case, we should keep `domain-fixed.pddl` and rename it to just `domain.pddl`.

What do you think @haz ?