agent: Re-group the options in the --help output.

* agent/gpg-agent.c (oGreeting): Remove non existant dummy option.

This looks better and is also required for further simplifications of
gpgconf.

(cherry picked from commit c693b7f4ade97357c33b410728bb741674255487)

• Signed-off-by: Werner Koch <wk@gnupg.org>