Remove config option B43_LEGACY_RFKILL completely

In f41f3f37 the B43 driver was ported
to use the cfg80211 API for rfkill and consequently the config option
was dropped (RFKILL is now unconditionally enabled).

However in the Kernel Info the feature is still checked and reported
missing. This patch just removes the conditional and the relevant code
blocks while still reporting that feature unconditionally would be
another option (it's always there).

Signed-off-by: Christoph Egger <siccegge@stud.informatik.uni-erlangen.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>