lib: deprecate node --debug at runtime

Fixes: https://github.com/nodejs/node/issues/9789
PR-URL: https://github.com/nodejs/node/pull/10970


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>