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

pkg/analyzer/lib/src/generated/parser.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 analyzer.src.generated.parser;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 280 matching lines @@
   void set enableNnbd(bool enable) {
     _enableNnbd = enable;
   }
 
   /**
    * Return `true` if the current token is the first token of a return type that
    * is followed by an identifier, possibly followed by a list of type
    * parameters, followed by a left-parenthesis. This is used by
    * [parseTypeAlias] to determine whether or not to parse a return type.
    */
-  @deprecated
   bool get hasReturnTypeInTypeAlias {
+    // TODO(brianwilkerson) This is too expensive as implemented and needs to be
+    // re-implemented or removed.
     Token next = skipReturnType(_currentToken);
     if (next == null) {
       return false;
     }
     return _tokenMatchesIdentifier(next);
   }
 
   /**
    * Set whether the parser is to parse the async support.
    *
@@ skipping 7807 matching lines @@
    */
   Parser_SyntheticKeywordToken(Keyword keyword, int offset)
       : super(keyword, offset);
 
   @override
   int get length => 0;
 
   @override
   Token copy() => new Parser_SyntheticKeywordToken(keyword, offset);
 }