scsi: scsi_dh_alua: remove synchronous STPG support

Since 9c58b395 ("scsi: scsi_devinfo: remove synchronous ALUA for NETAPP
devices") this code is unused.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>