doc: remove unnecessary intro in governance doc

The introductory paragraph in GOVERNANCE.md does not add anything that
isn't obvious from the document itself. Remove it.

PR-URL: https://github.com/nodejs/node/pull/27036


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>