Intl.RelativeTimeFormat: Test for grouping in long numbers.

The specification was changed to remove the useGrouping option in
<https://github.com/tc39/proposal-intl-relative-time/pull/81>.

The change to remove the minimumIntegerDigits option in that PR was already
taken into account; this commit also removes the reference to the issue.

This also removes some commented-out code that was left in by accident.