Remove som GYP annotations, remove unused manifest.

extensions/strings/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.
 
 import("//tools/grit/grit_rule.gni")
 
 assert(enable_extensions)
 
-# GYP version: extensions/extensions_strings.gyp:extensions_strings
 grit("strings") {
   # This target is in this directory since it matches the output grit path for
   # the GYP version of this target. Weirdly, it does not match the input path.
   # The .grd should probably be moved here.
   source = "../extensions_strings.grd"
   outputs = [
     "grit/extensions_strings.h",
     "extensions_strings_am.pak",
     "extensions_strings_ar.pak",
     "extensions_strings_bg.pak",
@@ skipping 43 matching lines @@
     "extensions_strings_ta.pak",
     "extensions_strings_te.pak",
     "extensions_strings_th.pak",
     "extensions_strings_tr.pak",
     "extensions_strings_uk.pak",
     "extensions_strings_vi.pak",
     "extensions_strings_zh-CN.pak",
     "extensions_strings_zh-TW.pak",
   ]
 }