Selinux: Remove unused headers slab.h in selinux/ss/symtab.c

slab.h is unused in symtab.c, so remove it.
Signed-off-by: Zhitong Wang <zhitong.wangzt@alibaba-inc.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/selinux/ss/symtab.c

@@ -4,7 +4,6 @@
  * Author : Stephen Smalley, <sds@epoch.ncsc.mil>
  */
 #include <linux/kernel.h>
-#include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/errno.h>
 #include "symtab.h"