remove unneeded legacy test

The legacy test wasn't really testing anything useful, just the plan
behavior with no diff in a module returned a module with no diff.
There's no reason to convert this to the new plans, since there's no
legacy behavior to match.

terraform/context_plan_test.go

@@ -1411,73 +1411,6 @@ func TestContext2Plan_moduleVarComputed(t *testing.T) {
 	}
 }
 
-func TestContext2Plan_nil(t *testing.T) {
-	m := testModule(t, "plan-nil")
-	p := testProvider("aws")
-	p.GetSchemaReturn = &ProviderSchema{
-		ResourceTypes: map[string]*configschema.Block{
-			"aws_instance": {
-				Attributes: map[string]*configschema.Attribute{
-					"nil": {Type: cty.String, Optional: true},
-				},
-			},
-		},
-	}
-	p.DiffFn = testDiffFn
-
-	ctx := testContext2(t, &ContextOpts{
-		Config: m,
-		ProviderResolver: providers.ResolverFixed(
-			map[string]providers.Factory{
-				"aws": testProviderFuncFixed(p),
-			},
-		),
-		State: mustShimLegacyState(&State{
-			Modules: []*ModuleState{
-				&ModuleState{
-					Path: rootModulePath,
-					Resources: map[string]*ResourceState{
-						"aws_instance.foo": &ResourceState{
-							Type: "aws_instance",
-							Primary: &InstanceState{
-								ID: "bar",
-							},
-						},
-					},
-				},
-			},
-		}),
-	})
-
-	plan, diags := ctx.Plan()
-	if diags.HasErrors() {
-		t.Fatalf("unexpected errors: %s", diags.Err())
-	}
-
-	if len(plan.Changes.Resources) != 1 {
-		t.Fatal("expected 1 changes, got", len(plan.Changes.Resources))
-	}
-	schema := p.GetSchemaReturn.ResourceTypes["aws_instance"]
-	ty := schema.ImpliedType()
-
-	for _, res := range plan.Changes.Resources {
-		if res.Action != plans.Update {
-			t.Fatalf("expected resource creation, got %s", res.Action)
-		}
-		ric, err := res.Decode(ty)
-		if err != nil {
-			t.Fatal(err)
-		}
-
-		switch i := ric.Addr.String(); i {
-		case "aws_instance.foo":
-			checkVals(t, cty.NullVal(schema.ImpliedType()), ric.After)
-		default:
-			t.Fatal("unknown instance:", i)
-		}
-	}
-}
-
 func TestContext2Plan_preventDestroy_bad(t *testing.T) {
 	m := testModule(t, "plan-prevent-destroy-bad")
 	p := testProvider("aws")

terraform/test-fixtures/plan-nil/main.tf

@@ -1,3 +0,0 @@
-resource "aws_instance" "foo" {
-    nil = "1"
-}