For now, the only serialization trait we were verifying
a polymorphic TTG type to have was the wrong (the one
that only printed base class's fields).
This commit explicitly disables said serializer and
ensures it's never used.
Here's an illustration of the impact of the changes:
```
model::UpcastableType MyType = getTypeFromSomewhere();
model::Type &View = *MyType;
model::PointerType &Pointer = MyType->asPointer();
serialize(MyType); // Good
serialize(Pointer); // Good
serialize(View); // new: explicit error
// old: only print base type's fields
```
Alessandro Di Federico