Remove `ignoreUnsupportedConstraintTraits` from integration test models (#2516)

* Remove `ignoreUnsupportedConstraintTraits` from integration test models

Now that constraint traits are supported in server SDKs (with some
corner case caveats, see
https://github.com/awslabs/smithy-rs/issues/1401), we can remove
`ignoreUnsupportedConstraintTraits` from the codegen config of the
integration test models.

* Bring back ignoreUnsupportedConstraintTraits in RestJsonValidation model