src: simplify node_worker.cc using new KVStore API

PR-URL: https://github.com/nodejs/node/pull/31773


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>