test: improve code in test-http-bind-twice.js

* use const instead of var for required modules
* use assert.strictEqual instead of assert.equal

PR-URL: https://github.com/nodejs/node/pull/10318


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>