smalloc: remove module

Bye bye, smalloc. I'm not sure why this was still here; it was removed
in 70d1f32f

 and hasn't worked since. It wasn't packaged in the
binary, either.

Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
PR-URL: https://github.com/nodejs/node/pull/3099