doc: remove extraneous "for example" text

No need to announce obvious example code as being example code. Remove
unneeded "for example" text as one small way to try to keep the docs
more concise..

PR-URL: https://github.com/nodejs/node/pull/18890


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matheus Marchini <matheus@sthima.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>