ruby: eliminate non-determinism from ruby.stats output

ruby: eliminate non-determinism from ruby.stats output

Get rid of non-deterministic "stats" in ruby.stats output
such as time & date of run, elapsed & CPU time used,
and memory usage.  These values cause spurious
miscomparisons when looking at output diffs (though
they don't affect regressions, since the regressions
pass/fail status currently ignores ruby.stats entirely).

Most of this information is already captured in other
places (time & date in stdout, elapsed time & mem usage
in stats.txt), where the regression script is smart
enough to filter it out.  It seems easier to get rid of
the redundant output rather than teaching the
regression tester to ignore the same information in
two different places.