staging: rtl8192u: remove unneeded SN_LESS macro

It's already in a .h file, don't redefine it as the compiler doesn't
like it if it does not match identically.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192u/ieee80211/ieee80211_tx.c

@@ -302,7 +302,6 @@ ieee80211_classify(struct sk_buff *skb, struct ieee80211_network *network)
 	}
 }
 
-#define SN_LESS(a, b)		(((a-b)&0x800)!=0)
 static void ieee80211_tx_query_agg_cap(struct ieee80211_device *ieee,
 				       struct sk_buff *skb, struct cb_desc *tcb_desc)
 {