Drop support for older Barback versions.

lib/src/asset/dart/serialize/aggregate_transform.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 pub.asset.serialize.aggregate_transform;
 
 import 'dart:async';
 import 'dart:isolate';
 
 import 'package:barback/barback.dart';
@@ skipping 102 matching lines @@
 
   void consumePrimary(AssetId id) {
     call(_port, {'type': 'consumePrimary', 'assetId': serializeId(id)});
   }
 }
 
 // We can get away with only removing the class declarations in incompatible
 // barback versions because merely referencing undefined types in type
 // annotations isn't a static error. Only implementing an undefined interface is
 // a static error.
-//# if barback >=0.14.1
 
 /// A wrapper for an [AggregateTransform] that's in the host isolate.
 ///
 /// This retrieves inputs from and sends outputs and logs to the host isolate.
 class ForeignAggregateTransform extends _ForeignBaseAggregateTransform
     with GetInputTransform implements AggregateTransform {
   final Stream<Asset> primaryInputs;
 
   /// Creates a transform from a serialized map sent from the host isolate.
   ForeignAggregateTransform(Map transform)
@@ skipping 28 matching lines @@
             transform['primaryIds'], deserializeId),
         super(transform);
 
   void declareOutput(AssetId id) {
     call(_port, {
       'type': 'declareOutput',
       'output': serializeId(id)
     });
   }
 }
-
-//# end