lib: use `validateObject`

Used the validateObject() validator to keep consistency instead of a
custom validator which was only used to validate objects.
Refs: #39595

PR-URL: https://github.com/nodejs/node/pull/39605
Refs: https://github.com/nodejs/node/pull/39595


Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>