src: remove AsyncScope and AsyncCallbackScope

Reduce the number of different scopes we use for async callbacks.

PR-URL: https://github.com/nodejs/node/pull/30236


Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>