Remove //third_party/iaccessible2.

third_party/iaccessible2/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("iaccessible2") {
-  sources = [
-    "ia2_api_all.idl",
-  ]
-}
-
-# Generate a proxy DLL from the generated code.
-shared_library("IAccessible2Proxy") {
-  sources = [
-    "IAccessible2Proxy.def",
-    "$target_gen_dir/ia2_api_all.dlldata.c",
-    "$target_gen_dir/ia2_api_all_p.c",
-  ]
-
-  defines = [ "REGISTER_PROXY_DLL" ]
-
-  libs = [ "rpcrt4.lib" ]
-
-  deps = [
-    ":iaccessible2",
-  ]
-}