D5561: revlog: always enable generaldelta on version 2 revlogs

[Yuya Nishihara]

> -        if self._initempty:
> -            # changelogs don't benefit from generaldelta
> +        if self._initempty and (self.version & 0xFFFF == revlog.REVLOGV1):
> +            # changelogs don't benefit from generaldelta.

Perhaps, `debugdeltachain()` and `debugrevlog()` has to be updated as well.
They peek `.version` attribute.