src: remove --noharmony_classes again

Now that V8 has been upgraded, remove the --noharmony_classes and
--noharmony_object_literals workarounds from commits a2751e3e and
4e58211b.

PR-URL: https://github.com/iojs/io.js/pull/490


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Fedor Indutny <fedor@indutny.com>
Reviewed-By: Kenan Sulayman <kenan@sly.mn>
Reviewed-By: Rod Vagg <rod@vagg.org>