delete observe from the repo

pkg/observe/lib/src/bind_property.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.bind_property;
-
-import 'dart:async';
-import 'package:observe/observe.dart';
-
-/// Forwards an observable property from one object to another. For example:
-///
-///     class MyModel extends Observable {
-///       StreamSubscription _sub;
-///       MyOtherModel _otherModel;
-///
-///       MyModel() {
-///         ...
-///         _sub = onPropertyChange(_otherModel, #value,
-///             () => notifyPropertyChange(#prop, oldValue, newValue);
-///       }
-///
-///       String get prop => _otherModel.value;
-///       set prop(String value) { _otherModel.value = value; }
-///     }
-///
-/// See also [notifyPropertyChange].
-// TODO(jmesserly): make this an instance method?
-StreamSubscription onPropertyChange(Observable source, Symbol sourceName,
-    void callback()) {
-  return source.changes.listen((records) {
-    for (var record in records) {
-      if (record is PropertyChangeRecord &&
-          (record as PropertyChangeRecord).name == sourceName) {
-        callback();
-        break;
-      }
-    }
-  });
-}