Remove the GetCaption dataprovider method

xfa/fwl/core/cfwl_checkbox.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "xfa/fwl/core/cfwl_checkbox.h"
 
 #include <memory>
 
@@ skipping 11 matching lines @@
   m_pIface = pdfium::MakeUnique<IFWL_CheckBox>(
       m_pApp, pdfium::MakeUnique<CFWL_WidgetProperties>(this));
 
   CFWL_Widget::Initialize();
 }
 
 void CFWL_CheckBox::SetBoxSize(FX_FLOAT fHeight) {
   m_fBoxHeight = fHeight;
 }
 
-void CFWL_CheckBox::GetCaption(IFWL_Widget* pWidget,
-                               CFX_WideString& wsCaption) {
-  wsCaption = L"Check box";
-}
-
 FX_FLOAT CFWL_CheckBox::GetBoxSize(IFWL_Widget* pWidget) {
   return m_fBoxHeight;
 }