[FrameworkBundle] Fix the same order bug for the serializer normalizers

RemoveUnusedFormHtmlSanitizerPass needs no priority: FormPass is registered by
this bundle too, at the same priority, so registering the removal above it is
what decides the order.

SerializerPass is different. SerializerBundle is a required bundle, so it is
built before this one and its pass lands ahead of everything registered here at
the default priority. Without a priority the normalizers are removed after they
have been collected into the serializer, leaving two dangling references
whenever symfony/property-access is absent.