Sema: Don't need to pass parent signature to OpenedArchetypeType::get()

Author: slavapestov

lib/Sema/ConstraintSystem.cpp

@@ -2617,7 +2617,7 @@ ConstraintSystem::getTypeOfMemberReference(
   } else if (baseObjTy->isExistentialType()) {
     auto openedArchetype =
         OpenedArchetypeType::get(baseObjTy->getCanonicalType(),
-                                 useDC->getGenericSignatureOfContext());
+                                 GenericSignature());
     OpenedExistentialTypes.insert(
         {getConstraintLocator(locator), openedArchetype});
     baseOpenedTy = openedArchetype;