src: remove redundant `JSStream::DoAfterWrite`

`Finish<WriteWrap>` already does the same thing and is
called immediately afterwards anyway.

PR-URL: https://github.com/nodejs/node/pull/17713


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>