crypto: refactor randomBytes()

Use the scrypt() infrastructure to reimplement randomBytes() and
randomFill() in a simpler manner.

PR-URL: https://github.com/nodejs/node/pull/20816


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>