b43legacy: remove wireless extensions inclusions

linux/wireless.h and net/iw_handler.h headers are
for wireless extensions only, so mac80211 drivers
shouldn't be including them.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>