Don't make wxToolBarToolBase::Set{Normal,Disabled}Bitmap() virtual.

There is no need for this, these methods are not supposed to be overridden as
they are only ever called by wxToolBar itself and making them virtual just
confused things.

See #16985.

include/wx/tbarbase.h

@@ -177,8 +177,8 @@ public:
 
     void Toggle() { Toggle(!IsToggled()); }
 
-    virtual void SetNormalBitmap(const wxBitmap& bmp) { m_bmpNormal = bmp; }
-    virtual void SetDisabledBitmap(const wxBitmap& bmp) { m_bmpDisabled = bmp; }
+    void SetNormalBitmap(const wxBitmap& bmp) { m_bmpNormal = bmp; }
+    void SetDisabledBitmap(const wxBitmap& bmp) { m_bmpDisabled = bmp; }
 
     virtual void SetLabel(const wxString& label) { m_label = label; }