test: remove extra console output from test-os.js

PR-URL: https://github.com/nodejs/node/pull/12654


Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>