Delete dartiverse-search from the repo and update dart:io documentation to point

samples/dartiverse_search/lib/search_engine.dart

-// Copyright (c) 2013, 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 search_engine;
-
-import 'dart:async';
-import 'dart:convert' show JSON;
-import 'dart:io' show HttpStatus;
-import 'package:http/http.dart' as http_client;
-
-part 'github_search_engine.dart';
-part 'stack_overflow_search_engine.dart';
-
-
-/**
- * A [SearchEngine] provides the ability to search for a given string.
- */
-abstract class SearchEngine {
-  /**
-   * Get the name of the search engine.
-   */
-  String get name;
-
-  /**
-   * Perform a search for [input]. The returned [Stream] will complete
-   * when there are no more results.
-   */
-  Stream<SearchResult> search(String input);
-}
-
-
-/**
- * A [SearchResult] entry, returned by [SearchEngine.search].
- */
-class SearchResult {
-  /**
-   * The title of the result.
-   */
-  final String title;
-
-  /**
-   * The link of the result.
-   */
-  final String link;
-
-  /**
-   * Create a new [SearchResult] from a title and a link.
-   */
-  SearchResult(this.title, this.link);
-}