test: do not force the process to exit

Using `process.exit()` in these tests is unnecessary and may mask other
problems.

Refs: https://github.com/nodejs/node/pull/29873#pullrequestreview-298851847

PR-URL: https://github.com/nodejs/node/pull/29923


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>