lib,src,test: update --debug/debug-brk comments

Overlooked in commit 47f8f746 ("src: remove support for --debug") from
earlier this month.

PR-URL: https://github.com/nodejs/node/pull/12495


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>