Remove unused sysbtn code

xfa/fwl/cfwl_sysbtn.cpp

-// Copyright 2016 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/cfwl_sysbtn.h"
-
-#include "xfa/fwl/cfwl_themepart.h"
-
-CFWL_SysBtn::CFWL_SysBtn() {
-  m_rtBtn.Set(0, 0, 0, 0);
-  m_dwState = 0;
-}
-
-CFWL_SysBtn::~CFWL_SysBtn() {}
-
-bool CFWL_SysBtn::IsDisabled() const {
-  return !!(m_dwState & FWL_SYSBUTTONSTATE_Disabled);
-}
-
-void CFWL_SysBtn::SetNormal() {
-  m_dwState &= 0xFFF0;
-}
-
-void CFWL_SysBtn::SetPressed() {
-  SetNormal();
-  m_dwState |= FWL_SYSBUTTONSTATE_Pressed;
-}
-
-void CFWL_SysBtn::SetHover() {
-  SetNormal();
-  m_dwState |= FWL_SYSBUTTONSTATE_Hover;
-}
-
-void CFWL_SysBtn::SetDisabled(bool bDisabled) {
-  bDisabled ? m_dwState |= FWL_SYSBUTTONSTATE_Disabled
-            : m_dwState &= ~FWL_SYSBUTTONSTATE_Disabled;
-}
-
-uint32_t CFWL_SysBtn::GetPartState() const {
-  if (IsDisabled())
-    return CFWL_PartState_Disabled;
-  if (m_dwState & FWL_SYSBUTTONSTATE_Pressed)
-    return CFWL_PartState_Pressed;
-  if (m_dwState & FWL_SYSBUTTONSTATE_Hover)
-    return CFWL_PartState_Hovered;
-  return CFWL_PartState_Normal;
-}