Remove `isApplicable` from the `StratifiedRule`s

[Kukovec]

Following the discussion under https://github.com/informalsystems/apalache/pull/2554#discussion_r1189995434, we should consider simplifying the rewriting rules, by making them return Options (or equivalent). Theoretically, this should suffice for the rewriter, under the assumption that there is at most one applicable rule for each input.