nl80211: remove duplicated #include

Remove duplicated #include in net/wireless/core.h.
Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/core.h

@@ -10,7 +10,6 @@
 #include <linux/netdevice.h>
 #include <linux/kref.h>
 #include <linux/rbtree.h>
-#include <linux/mutex.h>
 #include <net/genetlink.h>
 #include <net/wireless.h>
 #include <net/cfg80211.h>