qcow2: removed unused depends_on field

Signed-off-by: NFrediano Ziglio <freddy77@gmail.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/qcow2-cluster.c

@@ -694,7 +694,7 @@ err:
  * If the offset is not found, allocate a new cluster.
  *
  * If the cluster was already allocated, m->nb_clusters is set to 0,
- * m->depends_on is set to NULL and the other fields in m are meaningless.
+ * other fields in m are meaningless.
  *
  * If the cluster is newly allocated, m->nb_clusters is set to the number of
  * contiguous clusters that have been allocated. In this case, the other
@@ -736,7 +736,6 @@ again:
 
         cluster_offset &= ~QCOW_OFLAG_COPIED;
         m->nb_clusters = 0;
-        m->depends_on = NULL;
 
         goto out;
     }

block/qcow2.h

@@ -148,7 +148,6 @@ typedef struct QCowL2Meta
     int n_start;
     int nb_available;
     int nb_clusters;
-    struct QCowL2Meta *depends_on;
     CoQueue dependent_requests;
 
     QLIST_ENTRY(QCowL2Meta) next_in_flight;