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.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
documentation is changed or added -
commit message follows commit guidelines
Affected core subsystem(s)
test