lib: remove dollar symbol for private function

Just remove '$' because this isn't a programming language like Python.

PR-URL: https://github.com/nodejs/node/pull/25590


Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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