test: move common.fires() to inspector-helper

common.fires() is specific to the inspector tests so move it to
inspector-helper.js. The one REPL test that used common.fires() does not
seem to need it. It provided a 1 second timeout for operations, but that
timeout appears both arbitrary and ineffective as the test passes if it
is reduced to even 1 millisecond.

PR-URL: https://github.com/nodejs/node/pull/17401


Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>