Clean up duplicate includes in include/linux/memory_hotplug.h

This patch cleans up duplicate includes in
	include/linux/memory_hotplug.h
Signed-off-by: NJesper Juhl <jesper.juhl@gmail.com>
Acked-by: NYasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/memory_hotplug.h

@@ -3,7 +3,6 @@
 
 #include <linux/mmzone.h>
 #include <linux/spinlock.h>
-#include <linux/mmzone.h>
 #include <linux/notifier.h>
 
 struct page;