mac80211: remove deprecated API

All but two drivers have now stopped using the two
deprecated members radio_enabled and beacon_int,
so it's about time to remove them for good.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Kalle Valo <kalle.valo@iki.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>