Change IFWL_Widget to store a single delegate.

xfa/fxfa/app/xfa_ffcheckbutton.h

Index: xfa/fxfa/app/xfa_ffcheckbutton.h
diff --git a/xfa/fxfa/app/xfa_ffcheckbutton.h b/xfa/fxfa/app/xfa_ffcheckbutton.h
index 0c2cb755ac793faf7300f3896ef0bb591ef674eb..abb0ba084a3ead035087530448996f46c2bdffc2 100644
--- a/xfa/fxfa/app/xfa_ffcheckbutton.h
+++ b/xfa/fxfa/app/xfa_ffcheckbutton.h
@@ -25,10 +25,6 @@ class CXFA_FFCheckButton : public CXFA_FFField {
   FX_BOOL UpdateFWLData() override;
   void UpdateWidgetProperty() override;
   FX_BOOL OnLButtonUp(uint32_t dwFlags, FX_FLOAT fx, FX_FLOAT fy) override;
-  void OnProcessMessage(CFWL_Message* pMessage) override;
-  void OnProcessEvent(CFWL_Event* pEvent) override;
-  void OnDrawWidget(CFX_Graphics* pGraphics,
-                    const CFX_Matrix* pMatrix = nullptr) override;
 
   void SetFWLCheckState(XFA_CHECKSTATE eCheckState);
 
@@ -39,7 +35,6 @@ class CXFA_FFCheckButton : public CXFA_FFField {
   void CapLeftRightPlacement(CXFA_Margin mgCap);
   void AddUIMargin(int32_t iCapPlacement);
   XFA_CHECKSTATE FWLState2XFAState();
-  IFWL_WidgetDelegate* m_pOldDelegate;
   CFX_RectF m_rtCheckBox;
 };