This was added specifically for `ModDifficultyAdjust`, but turned out to
be more of a headache than we expected. We have since removed usage and
would hope that this is not required by any other mods.
Opting for complete removal rather than obsoletion, as we discovered
this was already broken in multiple cases, with fixes being quite
logically complex.
If you happen to be a ruleset developer relying on this, open an issue
and we'll talk you through a better approach (or check what
`ModDifficultyAdjust` is doing now for an example).
