src: remove calls to deprecated ArrayBuffer methods

v8::ArrayBuffer::IsExternal and v8::ArrayBuffer::Externalize are
no longer necessary.

PR-URL: https://github.com/nodejs/node/pull/32358


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>