don't use annoying and unneeded in C++ casts of NULL to "T *" in all other files neither

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58227 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/helpbase.h

@@ -82,7 +82,7 @@ public:
         wxPoint *WXUNUSED(pos) = NULL,
         bool *WXUNUSED(newFrameEachTime) = NULL)
     {
-        return (wxFrame*) NULL; // does nothing by default
+        return NULL; // does nothing by default
     }
 
     virtual bool Quit() = 0;