Upgrade to use stable `package:googleapis/v1.dart` of datastore

lib/db.dart

 // Copyright (c) 2014, 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 gcloud.db;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:mirrors' as mirrors;
 
-import 'common.dart' show Page, StreamFromPages;
+import 'common.dart' show StreamFromPages;
 import 'service_scope.dart' as ss;
 import 'datastore.dart' as datastore;
 
 part 'src/db/annotations.dart';
 part 'src/db/db.dart';
 part 'src/db/models.dart';
 part 'src/db/model_db.dart';
 part 'src/db/model_db_impl.dart';
 
 const Symbol _dbKey = #gcloud.db;
@@ skipping 11 matching lines @@
 ///
 /// The provided `db` object will be available via the top-level `dbService`
 /// getter.
 ///
 /// Calling this function outside of a service scope will result in an error.
 /// Calling this function more than once inside the same service scope is not
 /// allowed.
 void registerDbService(DatastoreDB db) {
   ss.register(_dbKey, db);
 }