treewide: remove DRIVER_11N_SUPPORT

hostapd's compile time option CONFIG_IEEE80211N was removed almost 3 years
ago, 80.211n/HT is always included since then.

Noticed because `hostapd -v11n` confusingly returned an error.

See hostapd's commit:
f3bcd69603 "Remove CONFIG_IEEE80211N build option"

Signed-off-by: Andre Heider <a.heider@gmail.com>

package/network/services/hostapd/src/src/utils/build_features.h

@@ -7,10 +7,6 @@ static inline int has_feature(const char *feat)
 	if (!strcmp(feat, "eap"))
 		return 1;
 #endif
-#ifdef CONFIG_IEEE80211N
-	if (!strcmp(feat, "11n"))
-		return 1;
-#endif
 #ifdef CONFIG_IEEE80211AC
 	if (!strcmp(feat, "11ac"))
 		return 1;