name-rev: make --stdin hidden

name-rev: make --stdin hidden

In 34ae3b70 (name-rev: deprecate --stdin in favor of --annotate-stdin),
we renamed --stdin to --annotate-stdin for the sake of a clearer name
for the option, and added text that indicates --stdin is deprecated. The
next step is to hide --stdin completely.

Make the option hidden. Also, update documentation to remove all
mentions of --stdin.

Signed-off-by: "John Cai" <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>