mm: remove duplicate include in hugepage-mremap.c

Remove duplicate includes 'unistd.h' included in
 '/tools/testing/selftests/vm/hugepage-mremap.c'  is duplicated.It is also
 included on 23 line.

Link: https://lkml.kernel.org/r/20211018102336.869726-1-ran.jianping@zte.com.cn
Signed-off-by: Ran Jianping <ran.jianping@zte.com.cn>
Reported-by: Zeal Robot <zealci@zte.com.cn>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/hugepage-mremap.c

@@ -15,7 +15,6 @@
 #include <errno.h>
 #include <fcntl.h> /* Definition of O_* constants */
 #include <sys/syscall.h> /* Definition of SYS_* constants */
-#include <unistd.h>
 #include <linux/userfaultfd.h>
 #include <sys/ioctl.h>