doc: remove **Note:** tags

Remove the various **Note:** prefixes throughout the docs.

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


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>