doc: remove experimental from --enable-source-maps

PR-URL: https://github.com/nodejs/node/pull/37540
Refs: https://github.com/nodejs/node/pull/37362


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>