delete observe from the repo

pkg/observe/lib/src/change_record.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-library observe.src.change_record;
-
-import 'package:observe/observe.dart';
-
-
-/// Records a change to an [Observable].
-// TODO(jmesserly): remove this type
-abstract class ChangeRecord {}
-
-/// A change record to a field of an observable object.
-class PropertyChangeRecord<T> extends ChangeRecord {
-  /// The object that changed.
-  final object;
-
-  /// The name of the property that changed.
-  final Symbol name;
-
-  /// The previous value of the property.
-  final T oldValue;
-
-  /// The new value of the property.
-  final T newValue;
-
-  PropertyChangeRecord(this.object, this.name, this.oldValue, this.newValue);
-
-  String toString() =>
-      '#<PropertyChangeRecord $name from: $oldValue to: $newValue>';
-}