Selinux: Remove unused headers skbuff.h in selinux/nlmsgtab.c

skbuff.h is already included by netlink.h, so remove it.
Signed-off-by: Zhitong Wang <zhitong.wangzt@alibaba-inc.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/selinux/nlmsgtab.c

@@ -11,7 +11,6 @@
  */
 #include <linux/types.h>
 #include <linux/kernel.h>
-#include <linux/skbuff.h>
 #include <linux/netlink.h>
 #include <linux/rtnetlink.h>
 #include <linux/if.h>