rev-list: make it obvious that we do not support notes

rev-list: make it obvious that we do not support notes

The rev-list command does not have the internal
infrastructure to display notes. Running:

  git rev-list --notes HEAD

will silently ignore the "--notes" option. Running:

  git rev-list --notes --grep=. HEAD

will crash on an assert. Running:

  git rev-list --format=%N HEAD

will place a literal "%N" in the output (it does not even
expand to an empty string).

Let's have rev-list tell the user that it cannot fill the
user's request, rather than silently producing wrong data.
Likewise, let's remove mention of the notes options from the
rev-list documentation.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>