test: refactor test/common/report.js

- Don't unnecessarily require('../common').
- Eliminate state maintained in tmppath.
- validate() was being used synchronously, but was actually
  asynchronous. Make it synchronous.
- Other misc. drive by cleanup.

PR-URL: https://github.com/nodejs/node/pull/25754


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>