doc: revise TSC Meetings material in GOVERNANCE.md

Make the TSC Meetings section in GOVERNANCE.md simpler and shorter.

PR-URL: https://github.com/nodejs/node/pull/27204


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>