Revert "Add support for building patched_sdk and platform.dill for dart2js:"

pkg/front_end/lib/src/fasta/parser/dart_vm_native.dart

 // Copyright (c) 2017, 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.
 
-/// Implements support for Dart VM native method bodies of this form:
+/// Implements support for Dart VM native method bodies on this form:
 ///
 ///     native STRING
 ///
 /// This support is kept separate from parser.dart as this isn't specified in
 /// the Dart Language Specification, also we hope to remove this syntax long
 /// term and replace it with annotations as in `dart2js`.
 library fasta.parser.dart_vm_native;
 
 import '../scanner/token.dart' show Token;
 
@@ skipping 30 matching lines @@
 Link<Token> removeNativeClause(Link<Token> identifiers) {
   Link<Token> result = identifiers.tail;
   if (result.head.kind != STRING_TOKEN) return identifiers;
   result = result.tail;
   if (result.isEmpty) return identifiers;
   if (optional('native', result.head)) {
     return result.tail.prepend(identifiers.head);
   }
   return identifiers;
 }