fs: remove unnecessary throw on fs.mkdtemp

The type is already checked in JS. Change to a CHECK

PR-URL: https://github.com/nodejs/node/pull/17334


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>