Remove som GYP annotations, remove unused manifest.

third_party/isimpledom/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 assert(is_win)
 
 import("//build/toolchain/win/midl.gni")
 
 midl("isimpledom") {
   sources = [
     "ISimpleDOMDocument.idl",
     "ISimpleDOMNode.idl",
     "ISimpleDOMText.idl",
   ]
-  # Note: GYP version sets 'GenerateTypeLibrary': 'false'. It doesn't seem to
-  # be harmful to generate this, however.
 }