test: fix test/pummel/test-fs-watch-file.js

test-fs-watch-file.js fails for two reasons. First, there are cases
where it is checking the error message for an error whose message has
changed since the test was written. Change these instances to check for
an error code instead.

Second, there is an instance where it tries to remove a listener but
fails because `common.mustNotCall()` returns a differnet instance of a
function on each call. Store the function in a variable name so it can
be removed as a listener on a file.

PR-URL: https://github.com/nodejs/node/pull/25384


Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>