[libata] remove redundant use of ATA_QCFLAG_SG in ATAPI packet translation

ata_scsi_translate() sets this flag for all ATA->SCSI translated
commands, so it need not be done in atapi_xlat().  The now-removed
use in atapi_xlat() was also inconsistent WRT PIO versus DMA.

drivers/scsi/libata-scsi.c

@@ -924,7 +924,6 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc, u8 *scsicmd)
 
 	/* DMA data xfer - interrupt-driven */
 	} else {
-		qc->flags |= ATA_QCFLAG_SG; /* data is present; dma-map it */
 		qc->tf.protocol = ATA_PROT_ATAPI_DMA;
 		qc->tf.feature |= ATAPI_PKT_DMA;