Remove validations

Two reasons for this:

1. Validations have nothing to do with persistence. If you want to restrict the values of your objects' attributes, this should be done on the domain model before persistence even becomes a concern. The only persistence-level concern for validations is uniqueness (since this cannot be validated on individual objects), which are covered by unique indexes rather than validations.
2. Validations in Perpetuity were so minimal that a lot of times you had to implement your own validations on your objects anyway.