Clear unavailable validations

[belozer-ti]

I found bug at the contentful models.
Many models have incorrect validation references.

How its happens:

1. create model A
2. create model B
3. create references field (e.g. category) at the model A
4. go to settings of category field and add validation Accept only specified entry type to model B
5. save and check json preview
6. go to model B and delete this model
7. go back to model A and check json preview.
8. validation continues to refer to model B, but model B already deleted
9. run codegen

In results we will have links to non-existent interfaces and generated code will be broken.

I think this problem on the contentful side.... But maybe need fix it on codegen side?