doc: simplify and correct example descriptions in net.md

Instead of indicating that examples show lines to change in previous
examples, present the examples as standalone items. They suffice on
their own.

In the first of these, it says to change "the second line" of a previous
example, but if it were literally changed to the provided line, it would
result in a syntax error.

In the second of these, it gives the wrong line to change.

All of this is unnecessary and probably makes the examples harder to
follow. So simplify and treat each one as a separate example.

PR-URL: https://github.com/nodejs/node/pull/32451


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>