gpgconf: Swap "auto-key-retrieve" and "no-auto-key-retrieve".

* g10/gpg.c (gpgconf_list): Announce "auto-key-retrieve".
(main): Simplify setting of KEYSERVER_AUTO_KEY_RETRIEVE.
* tools/gpgconf-comp.c: Make "no-auto-key-retrieve" invisible.  Make
"auto-key-retrieve" an expert option.

This basically reverts 9bb13a0e819334681caca38c9074bd7bfc04e45e
because --no-auto-key-retrieve is again the default. Note that we
allow both options for the sake of profiles.

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