ObjectTypeDB was renamed to ClassDB. Types are meant to be more generic to Variant.

All usages of "type" to refer to classes were renamed to "class"
ClassDB has been exposed to GDScript.
OBJ_TYPE() macro is now GDCLASS()

core/reference.h

@@ -39,7 +39,7 @@
 */
 class Reference : public Object{
 
-	OBJ_TYPE( Reference, Object );
+	GDCLASS( Reference, Object );
 friend class RefBase;
 	SafeRefCount refcount;
 	SafeRefCount refcount_init;
@@ -315,7 +315,7 @@ typedef Ref<Reference> REF;
 
 class WeakRef : public Reference {
 
-	OBJ_TYPE(WeakRef,Reference);
+	GDCLASS(WeakRef,Reference);
 
 	ObjectID ref;
 protected: