rename completion source files to match content

pkg/analysis_server/lib/src/services/completion/local_reference_contributor.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 services.completion.contributor.dart.local;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol.dart' as protocol
     show Element, ElementKind;
@@ skipping 680 matching lines @@
   bool _isVoid(TypeName returnType) {
     if (returnType != null) {
       Identifier id = returnType.name;
       if (id != null && id.name == 'void') {
         return true;
       }
     }
     return false;
   }
 }