Way back we've added `common.math.BigMin` and `common.math.BigMax`.
These were kind of cute helpers, but unfortunate ones, because package
all over out codebase added dependencies to this package just to avoid
having to write out 3 lines of code.
Because of this, we've also started having package name clashes with the
stdlib `math`, which got solves even more badly by moving some helpers
over ***from*** the stdlib into our custom lib (e.g. MaxUint64). The
latter ones were nuked out in a previous PR and this PR nukes out BigMin
and BigMax, inlining them at all call sites.
As we're transitioning to uint256, if need be, we can add a min and max
to that.
