mm/slab.h: remove duplicate include

Remove duplicate header which is included twice.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Link: http://lkml.kernel.org/r/20200818114323.58156-1-yuehaibing@huawei.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slab.h

@@ -46,7 +46,6 @@ struct kmem_cache {
 #include <linux/kmemleak.h>
 #include <linux/random.h>
 #include <linux/sched/mm.h>
-#include <linux/kmemleak.h>
 
 /*
  * State of the slab allocator.