Revert "[ConstantRange] Rename make{Guaranteed -> Exact}NoWrapRegion() NFC"

This reverts commit 7bf4d7c07f2fac862ef34c82ad0fef6513452445.

After thinking about this more, this isn't right, the range is not exact
in the same sense as makeExactICmpRegion(). This needs a separate
function.

llvm-svn: 358876