remove some destroy special cases

We no longer need special cases for most things during a full destroy,
so remove those from the graph transformations.

The only remaining cases are:
 - remove the root outputs, so destroy ends up with a clean state
 - reverse the target deps when targeting a destroy.

terraform/graph_builder_apply.go

@@ -168,16 +168,10 @@ func (b *ApplyGraphBuilder) Steps() []GraphTransformer {
 			Config:  b.Config,
 			State:   b.State,
 			Schemas: b.Schemas,
-			Destroy: b.Destroy,
 		},
 
-		GraphTransformIf(
-			func() bool { return b.Destroy },
-			GraphTransformMulti(
-				// Create a destroy node for outputs to remove them from the state.
-				&DestroyOutputTransformer{},
-			),
-		),
+		// Create a destroy node for outputs to remove them from the state.
+		&DestroyOutputTransformer{Destroy: b.Destroy},
 
 		// Prune unreferenced values, which may have interpolations that can't
 		// be resolved.

terraform/transform_destroy_cbd.go

@@ -134,16 +134,9 @@ type CBDEdgeTransformer struct {
 	// obtain schema information from providers and provisioners so we can
 	// properly resolve implicit dependencies.
 	Schemas *Schemas
-
-	// If the operation is a simple destroy, no transformation is done.
-	Destroy bool
 }
 
 func (t *CBDEdgeTransformer) Transform(g *Graph) error {
-	if t.Destroy {
-		return nil
-	}
-
 	// Go through and reverse any destroy edges
 	for _, v := range g.Vertices() {
 		dn, ok := v.(GraphNodeDestroyerCBD)

terraform/transform_output.go

@@ -60,9 +60,15 @@ func (t *OutputTransformer) transform(g *Graph, c *configs.Config) error {
 // outputs during destroy. We need to do this to ensure that no stale outputs
 // are ever left in the state.
 type DestroyOutputTransformer struct {
+	Destroy bool
 }
 
 func (t *DestroyOutputTransformer) Transform(g *Graph) error {
+	// Only clean root outputs on a full destroy
+	if !t.Destroy {
+		return nil
+	}
+
 	for _, v := range g.Vertices() {
 		output, ok := v.(*NodeApplyableOutput)
 		if !ok {