This is an editorial change in the Temporal spec. See:
https://github.com/tc39/proposal-temporal/commit/1b051cc
Note that since Date's implementation of this AO uses Crypto bigints
rather than allocating JS bigints, this change has the fallout of
removing some unused VM parameters and adding an overload of the
IsValidEpochNanoseconds AO for use without a JS::BigInt.