legacy: print removal date in menuconfig

Show the user how old the legacy options are, as a
subtle suggestion for him to update mopre often. ;-)

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>