Remove unused variable from struct hostapd_config

I think that the "radius" pointer in the structure hostapd_config is
never used; when the configuration is parsed the related data is stored
in hostapd_bss_config's "radius" var.

hostapd/config.h

@@ -329,7 +329,6 @@ typedef enum {
  */
 struct hostapd_config {
 	struct hostapd_bss_config *bss, *last_bss;
-	struct hostapd_radius_servers *radius;
 	size_t num_bss;
 
 	u16 beacon_int;