GDScript: Remove self static reference and create one on calls

This is needed because of the new changes to Variant. The reference
counter is increased by adding it to a Variant, which means no GDScript
will be freed (or will be double freed if manually freed somewhere).

modules/gdscript/gdscript.h

@@ -73,7 +73,6 @@ class GDScript : public Script {
 	friend class GDScriptFunctions;
 	friend class GDScriptLanguage;
 
-	Variant _static_ref; //used for static call
 	Ref<GDScriptNativeClass> native;
 	Ref<GDScript> base;
 	GDScript *_base; //fast pointer access