doc: remove _Node.js style callback_

We refer to them only as _error-first callbacks_ in our docs. We don't
call them _Node.js style callbacks_ so let's take this opporutnity to
keep things a bit more concise

PR-URL: https://github.com/nodejs/node/pull/21701


Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>