test: simplify test-https-simple.js

It had an unused `Agent` option (no such option exists), and some code
that common.must(Not)Call makes redundant.

PR-URL: https://github.com/nodejs/node/pull/31584


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>