doc: remove notice of dashes in V8 options

Previously only V8 options supported both dashes in them (making them
equivalent), but now Node.js also supports both styles so the note can
be removed.

PR-URL: https://github.com/nodejs/node/pull/23903
Refs: https://github.com/nodejs/node/pull/18592


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: George Adams <george.adams@uk.ibm.com>