block/vhdx: drop unallocated_blocks_are_zero

vhdx doesn't have .bdrv_co_block_status handler, so DATA|ALLOCATED is
always assumed for it in bdrv_co_block_status().
unallocated_blocks_are_zero is useless (it doesn't affect the only user
of the field: bdrv_co_block_status()), drop it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200528094405.145708-9-vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
diff --git a/block/vhdx.c b/block/vhdx.c
index fa9e544..645dc4b 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -1164,9 +1164,6 @@
 
     bdi->cluster_size = s->block_size;
 
-    bdi->unallocated_blocks_are_zero =
-        (s->params.data_bits & VHDX_PARAMS_HAS_PARENT) == 0;
-
     return 0;
 }