test: refactor test-stream-transform-object

* use common.mustCall() as appropriate
* eliminate exit handler
* var -> const/let
* provide duration for setInterval()

PR-URL: https://github.com/nodejs/node/pull/10588


Reviewed-By: Italo A. Casas <me@italoacasas.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>