Remove include only fwl.h and IWYU.

BUILD.gn

 # Copyright 2016 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("//build_overrides/v8.gni")
 import("//testing/test.gni")
 import("pdfium.gni")
 
 config("pdfium_config") {
   cflags = []
@@ skipping 790 matching lines @@
       "xfa/include/fwl/core/fwl_grid.h",
       "xfa/include/fwl/core/fwl_note.h",
       "xfa/include/fwl/core/fwl_panel.h",
       "xfa/include/fwl/core/fwl_target.h",
       "xfa/include/fwl/core/fwl_theme.h",
       "xfa/include/fwl/core/fwl_thread.h",
       "xfa/include/fwl/core/fwl_timer.h",
       "xfa/include/fwl/core/fwl_widget.h",
       "xfa/include/fwl/core/fwl_widgetdef.h",
       "xfa/include/fwl/core/fwl_widgetmgr.h",
-      "xfa/include/fwl/fwl.h",
       "xfa/include/fwl/lightwidget/app.h",
       "xfa/include/fwl/lightwidget/barcode.h",
       "xfa/include/fwl/lightwidget/caret.h",
       "xfa/include/fwl/lightwidget/checkbox.h",
       "xfa/include/fwl/lightwidget/combobox.h",
       "xfa/include/fwl/lightwidget/datetimepicker.h",
       "xfa/include/fwl/lightwidget/edit.h",
       "xfa/include/fwl/lightwidget/listbox.h",
       "xfa/include/fwl/lightwidget/picturebox.h",
       "xfa/include/fwl/lightwidget/pushbutton.h",
@@ skipping 691 matching lines @@
       "//v8:v8_libplatform",
     ]
     include_dirs += [
       "//v8",
       "//v8/include",
     ]
     configs += [ "//v8:external_startup_data" ]
   }
   configs += [ ":pdfium_config" ]
 }