block/iscsi: drop unused IscsiAIOCB->buf field

The IscsiAIOCB->buf field has not been used since commit
e49ab19f ("block/iscsi: bump libiscsi
requirement to 1.9.0").  It used to be a linear buffer for old libiscsi
versions that didn't support scatter-gather.  The minimum libiscsi
version supports scatter-gather so we don't linearize buffers anymore.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20180203061621.7033-2-stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

block/iscsi.c

@@ -117,7 +117,6 @@ typedef struct IscsiAIOCB {
     QEMUBH *bh;
     IscsiLun *iscsilun;
     struct scsi_task *task;
-    uint8_t *buf;
     int status;
     int64_t sector_num;
     int nb_sectors;
@@ -150,9 +149,6 @@ iscsi_bh_cb(void *p)
 
     qemu_bh_delete(acb->bh);
 
-    g_free(acb->buf);
-    acb->buf = NULL;
-
     acb->common.cb(acb->common.opaque, acb->status);
 
     if (acb->task != NULL) {
@@ -933,9 +929,6 @@ iscsi_aio_ioctl_cb(struct iscsi_context *iscsi, int status,
 {
     IscsiAIOCB *acb = opaque;
 
-    g_free(acb->buf);
-    acb->buf = NULL;
-
     acb->status = 0;
     if (status < 0) {
         error_report("Failed to ioctl(SG_IO) to iSCSI lun. %s",
@@ -1010,7 +1003,6 @@ static BlockAIOCB *iscsi_aio_ioctl(BlockDriverState *bs,
     acb->iscsilun = iscsilun;
     acb->bh          = NULL;
     acb->status      = -EINPROGRESS;
-    acb->buf         = NULL;
     acb->ioh         = buf;
 
     if (req != SG_IO) {