src: remove unused fields from IsolateData

PR-URL: https://github.com/nodejs/node/pull/34139


Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: James M Snell <jasnell@gmail.com>