Remove wxHAS_PAINT_DEBUG and code guarded by it

This doesn't seem to actually be doing anything useful, as it only
checks that wxPaintDCImpl is not created without creating wxPaintDC
which is impossible to do accidentally anyhow.

This will be replaced by a more useful check in the next commit.

include/wx/event.h

@@ -2335,39 +2335,15 @@ private:
  wxEVT_NC_PAINT
  */
 
-#if wxDEBUG_LEVEL && defined(__WXMSW__)
-    #define wxHAS_PAINT_DEBUG
-
-    // see comments in src/msw/dcclient.cpp where g_isPainting is defined
-    extern WXDLLIMPEXP_CORE int g_isPainting;
-#endif // debug
-
 class WXDLLIMPEXP_CORE wxPaintEvent : public wxEvent
 {
 public:
     wxPaintEvent(int Id = 0)
         : wxEvent(Id, wxEVT_PAINT)
     {
-#ifdef wxHAS_PAINT_DEBUG
-        // set the internal flag for the duration of redrawing
-        g_isPainting++;
-#endif // debug
     }
 
-    // default copy ctor and dtor are normally fine, we only need them to keep
-    // g_isPainting updated in debug build
-#ifdef wxHAS_PAINT_DEBUG
-    wxPaintEvent(const wxPaintEvent& event)
-            : wxEvent(event)
-    {
-        g_isPainting++;
-    }
-
-    virtual ~wxPaintEvent()
-    {
-        g_isPainting--;
-    }
-#endif // debug
+    // default copy ctor and dtor are fine
 
     virtual wxEvent *Clone() const wxOVERRIDE { return new wxPaintEvent(*this); }