process: remove deprecated process.EventEmitter

process.EventEmitter was deprecated for v6. This commit removes
it for v7.

Refs: https://github.com/nodejs/node/pull/5049
PR-URL: https://github.com/nodejs/node/pull/6862


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>