Revert "Package map source factory support" [TBR].

pkg/analyzer/lib/file_system/file_system.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 file_system;
 
 import 'dart:async';
 
 import 'package:analyzer/src/generated/source.dart';
 import 'package:path/path.dart';
@@ skipping 121 matching lines @@
  * Instances of the class [ResourceProvider] convert [String] paths into
  * [Resource]s.
  */
 abstract class ResourceProvider {
   /**
    * Get the path context used by this resource provider.
    */
   Context get pathContext;
 
   /**
-   * Return a [File] that corresponds to the given [path].
-   * 
-   * A file may or may not exist at this location.
-   */
-  File getFile(String path);
-
-  /**
-   * Return a [Folder] that corresponds to the given [path].
-   * 
-   * A folder may or may not exist at this location.
-   */
-  Folder getFolder(String path);
-
-  /**
    * Return the [Resource] that corresponds to the given [path].
    */
   Resource getResource(String path);
 
   /**
    * Return the folder in which the plugin with the given [pluginId] can store
    * state that will persist across sessions. The folder returned for a given id
    * will not be returned for a different id, ensuring that plugins do not need
    * to be concerned with file name collisions with other plugins, assuming that
    * the plugin ids are unique. The plugin ids must be valid folder names.
@@ skipping 28 matching lines @@
   }
 
   @override
   Uri restoreAbsolute(Source source) => source.uri;
 
   /**
    * Return `true` if the given [uri] is a `file` URI.
    */
   static bool _isFileUri(Uri uri) => uri.scheme == _FILE_SCHEME;
 }