Remove CG(active_class_entry) = NULL;

This has been in the code for a really long time, and doesn't seem
to be required now.  It's not documented by PHP as something we
need to do, and the value seems to always be NULL at this point
already.

Source/Modules/php.cxx

@@ -530,8 +530,6 @@ public:
      */
 
     //    Printv(s_init,s_resourcetypes,NIL);
-    /* We need this after all classes written out by ::top */
-    Printf(s_oinit, "  CG(active_class_entry) = NULL;\n");
     Printf(s_oinit, "  /* end oinit subsection */\n");
     Printf(s_init, "%s\n", s_oinit);