worker: improve JS-side debugging

Do not print debug messages that indicate that a stdio stream
has drained; because `util.debuglog()` uses `console.log`, which
in turn uses stdio streams, this would otherwise have lead to an
endless loop.

PR-URL: https://github.com/nodejs/node/pull/25312


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