Zapping is triggered by xkb these days, so note in the man page that it's the
Terminate_Server action. Since it's XKB, personal preferences towards or
against zapping should be achieved through xkb rulesets.
If Terminate_Server is not in the xkb actions, then we can't zap anyway and we
don't need a default of DontZap "on".

This patch restores the old meaning of DontZap - disallow zapping altogether,
regardless of XKB's current keymap.
Ideally, this patch should be accompanied by b0f64bdab00db652e in
xkeyboard-config.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>