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/thread.h

@@ -506,7 +506,7 @@ public:
         // does it!
         //
         // will fill the rc pointer with the thread exit code if it's !NULL
-    wxThreadError Delete(ExitCode *rc = (ExitCode *)NULL);
+    wxThreadError Delete(ExitCode *rc = NULL);
 
         // waits for a joinable thread to finish and returns its exit code
         //