destroy nodes can't be referenced directly

Destroy nodes were being referenced by their regular paths, which was
causing cycles in the graphs. Destroy nodes can't be referenced directly
in any way, so override the inherited method for a referenceable address.

terraform/node_resource_destroy.go

@@ -71,6 +71,12 @@ func (n *NodeDestroyResourceInstance) ReferenceableName() []addrs.Referenceable
 	}
 }
 
+// Destroy nodes can't be directly referenced by anything, so we need to
+// override the abstract method.
+func (n *NodeDestroyResourceInstance) ReferenceableAddrs() []addrs.Referenceable {
+	return nil
+}
+
 // GraphNodeReferencer, overriding NodeAbstractResource
 func (n *NodeDestroyResourceInstance) References() []*addrs.Reference {
 	// If we have a config, then we need to include destroy-time dependencies