make Changes.Empty() not count NoOps

This make the plan `Empty` concept more closely match the legacy diff
behavior.

Remove old unknown field from plan_test

plans/changes.go

@@ -32,7 +32,12 @@ func NewChanges() *Changes {
 }
 
 func (c *Changes) Empty() bool {
-	return (len(c.Resources) + len(c.Outputs)) == 0
+	for _, res := range c.Resources {
+		if res.Action != NoOp {
+			return false
+		}
+	}
+	return true
 }
 
 // ResourceInstance returns the planned change for the current object of the

plans/plan_test.go

@@ -13,7 +13,6 @@ func TestProviderAddrs(t *testing.T) {
 	plan := &Plan{
 		VariableValues: map[string]DynamicValue{},
 		Changes: &Changes{
-			RootOutputs: map[string]*OutputChangeSrc{},
 			Resources: []*ResourceInstanceChangeSrc{
 				{
 					Addr: addrs.Resource{