Remove package imports from itself.

pkg/front_end/lib/src/fasta/source/unhandled_listener.dart

 // Copyright (c) 2016, 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 fasta.unhandled_listener;
 
-import 'package:front_end/src/fasta/scanner/token.dart' show Token;
+import '../scanner/token.dart' show Token;
 
 import 'stack_listener.dart' show NullValue, StackListener;
 
 export 'stack_listener.dart' show NullValue;
 
 // TODO(ahe): Get rid of this.
 enum Unhandled {
   ConditionalUri,
   ConditionalUris,
   DottedName,
@@ skipping 49 matching lines @@
     push(popList(count) ?? NullValue.Combinators);
   }
 
   @override
   void endDottedName(int count, Token firstIdentifier) {
     debugEvent("DottedName");
     popList(count);
     push(Unhandled.DottedName);
   }
 }