ovl: remove duplicated include from super.c

Remove duplicated include.
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/super.c

@@ -16,7 +16,6 @@
 #include <linux/slab.h>
 #include <linux/parser.h>
 #include <linux/module.h>
-#include <linux/pagemap.h>
 #include <linux/sched.h>
 #include <linux/statfs.h>
 #include <linux/seq_file.h>