remove CompletionCache and obsolete tests, and cleanup imports

pkg/analysis_server/lib/src/services/completion/completion_manager.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.manager;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart'
     show CompletionContributor, CompletionContributorFactory, CompletionRequest, CompletionResult;
 import 'package:analysis_server/src/services/completion/dart_completion_manager.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 
 /**
- * [CompletionCache] contains information about the prior code completion
- * for use in the next code completion.
- */
-abstract class CompletionCache {
-  /**
-   * The context in which the completion was computed.
-   */
-  final AnalysisContext context;
-
-  /**
-   * The source in which the completion was computed.
-   */
-  final Source source;
-
-  CompletionCache(this.context, this.source);
-}
-
-/**
  * Manages completion contributors for a given completion request.
  */
 abstract class CompletionManager {
   /**
    * The context in which the completion was computed.
    */
   final AnalysisContext context;
 
   /**
    * The source in which the completion was computed.
@@ skipping 225 matching lines @@
    */
   final String name;
 
   /**
    * The elapse time or `null` if undefined.
    */
   final Duration elapsed;
 
   OperationPerformance(this.name, this.elapsed);
 }