This change removes `clockRate` precalculation from
`DifficultyCalculator`.
The idea is that clock rate should be calculated in-place (ideally for
every object) since we store and access it using DHOs. This also
prevents anyone from accidentally passing clock rate to skills
Unfortunately osu uses clock rate to calculate OD for the whole map in
`CreateDifficultyAttributes` so we can't make it completely DHO-based,
but I think one single in-place call to `ModUtils.CalculateRateWithMods`
in `CreateDifficultyAttributes` is fine
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Co-authored-by: James Wilson <tsunyoku@gmail.com>