Un-deprecate some deprecated code and fix a couple of hints

pkg/analyzer/lib/src/context/builder.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 analyzer.src.context.context_builder;
 
 import 'dart:collection';
 import 'dart:core';
 
 import 'package:analyzer/context/declared_variables.dart';
@@ skipping 59 matching lines @@
 
   /**
    * The options used by the context builder.
    */
   final ContextBuilderOptions builderOptions;
 
   /**
    * The resolver provider used to create a package: URI resolver, or `null` if
    * the normal (Package Specification DEP) lookup mechanism is to be used.
    */
-  @deprecated
   ResolverProvider packageResolverProvider;
 
   /**
    * The resolver provider used to create a file: URI resolver, or `null` if
    * the normal file URI resolver is to be used.
    */
-  @deprecated
   ResolverProvider fileResolverProvider;
 
   /**
    * Initialize a newly created builder to be ready to build a context rooted in
    * the directory with the given [rootDirectoryPath].
    */
   ContextBuilder(this.resourceProvider, this.sdkManager, this.contentCache,
       {ContextBuilderOptions options})
       : builderOptions = options ?? new ContextBuilderOptions();
 
@@ skipping 517 matching lines @@
   String _readEmbedderYaml(Folder libDir) {
     File file = libDir.getChild(EMBEDDER_FILE_NAME);
     try {
       return file.readAsStringSync();
     } on FileSystemException {
       // File can't be read.
       return null;
     }
   }
 }