tools: remove simplejson dependency

As Node.js expects either Python 2.6 or 2.7 installed to work properly,
simplejson module is no longer necessary. It was included in Python 2.6
as the json module.

PR-URL: https://github.com/nodejs/node/pull/6101


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>