Removed duplicated includes

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Closes #11775

cmd/zpool/os/linux/zpool_vdev_os.c

@@ -79,9 +79,6 @@
 
 #include <scsi/scsi.h>
 #include <scsi/sg.h>
-#include <stdio.h>
-#include <string.h>
-#include <unistd.h>
 #include <sys/efi_partition.h>
 #include <sys/stat.h>
 #include <sys/vtoc.h>