doc: remove extraneous sentence in events.md

Since the previous sentence describes `10` as a default, and the
following sentence explains how to modify that default, it is
unnecessary to explain that "Obviously, not all events should be limited
to just 10 listeners."

PR-URL: https://github.com/nodejs/node/pull/32457


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>