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/[e-mail]
Signed-off-by: Ran Jianping <[e-mail]>
Reported-by: Zeal Robot <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

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

···
 #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>