scsi: scsi_netlink: remove duplicate GPL boilerplate text

The SCSI netlink uapi header already has a proper SPDX tag, remove the
duplicate boilerplate text.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>