doc: revise "Breaking Changes" section of Collaborator Guide

Simplify material about TSC approval for breaking changes. Omit
extraneous material explaining that purely additive changes are not
breaking changes.

PR-URL: https://github.com/nodejs/node/pull/25071


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yuta Hiroto <hello@hiroppy.me>
Reviewed-By: James M Snell <jasnell@gmail.com>