test: use mustCall() in test-readline-interface

Use `common.mustCall()` to make sure noop function is called as
expected.

PR-URL: https://github.com/nodejs/node/pull/13259


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>