Staging: wlan-ng: remove dependency on WIRELESS_EXT version

As the driver is in mainline now we can remove such dependency.
WIRELESS_EXT is 22 now and it is always defined.

Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>