kconfig: nconf: rewrite labels of function keys line

>From: Roland Eggner <edvx1@systemanalysen.net>

More reasonable labels of function keys line.  Rename labels and keep menu
width, as required for fitting on COLUMNS=80 terminals:
•  s/Insts/Help 2/
•  s/Config/ShowAll/

Signed-off-by: Roland Eggner <edvx1@systemanalysen.net>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>