Clarify relation between trivial HasHardForkHistory instance and NoHardForks

~Remove it from `RunNode` and use `InFuture.miracle` when used with a single era/block.~

Let's introduce:
```haskell
trivialHardForkSummary :: NoHardForks blk => ..
```
And let `HasHardForkHistory` default (default instance or deriving via) to it when `NoHardForks blk` holds:
```haskell
hardForkSummary _ _ = trivialHardForkSummary
```

This is less ambitious than the first plan. `InFuture.reference` will still be used even for a single era/block.