Remove IWFL_WidgetMgr in favor of CFWL_WidgetMgr

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 1034 matching lines @@
       "xfa/fwl/core/fwl_widgetmgrimp.cpp",
       "xfa/fwl/core/fwl_widgetmgrimp.h",
       "xfa/fwl/core/ifwl_app.h",
       "xfa/fwl/core/ifwl_dataprovider.h",
       "xfa/fwl/core/ifwl_form.h",
       "xfa/fwl/core/ifwl_themeprovider.h",
       "xfa/fwl/core/ifwl_timer.h",
       "xfa/fwl/core/ifwl_tooltiptarget.h",
       "xfa/fwl/core/ifwl_widget.h",
       "xfa/fwl/core/ifwl_widgetdelegate.h",
-      "xfa/fwl/core/ifwl_widgetmgr.h",
       "xfa/fwl/core/include/fwl_widgethit.h",
       "xfa/fwl/core/include/ifwl_adaptertimermgr.h",
       "xfa/fwl/lightwidget/cfwl_barcode.cpp",
       "xfa/fwl/lightwidget/cfwl_barcode.h",
       "xfa/fwl/lightwidget/cfwl_checkbox.cpp",
       "xfa/fwl/lightwidget/cfwl_checkbox.h",
       "xfa/fwl/lightwidget/cfwl_combobox.cpp",
       "xfa/fwl/lightwidget/cfwl_combobox.h",
       "xfa/fwl/lightwidget/cfwl_datetimepicker.cpp",
       "xfa/fwl/lightwidget/cfwl_datetimepicker.h",
@@ skipping 643 matching lines @@
 }
 
 if (pdf_is_standalone) {
   source_set("samples") {
     testonly = true
     deps = [
       "//samples",
     ]
   }
 }