Update comments on ControllerRevision.Data

Author: Kenneth Owens

contributors/design-proposals/controller_history.md

@@ -131,8 +131,7 @@ type ControllerRevision struct {
     metav1.TypeMeta
     // +optional
     metav1.ObjectMeta
-    // Data is a map of keys to the serialized objects that comprise the state 
-    // snapshot.
+    // Data contains the serialized state.
     Data runtime.RawExtension
     // Revision indicates the revision of the state represented by Data.
     Revision int64