How to Remove an Endpoint Created From a Uniqueness Constraint
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### Summary

I'm using Postgraphile 4, and have a `users` table with an `email` column and a `UNIQUE` constraint (`users_email_unique`) on that column.  This generates a `userByEmail` endpoint in GraphQL...  which I would like to remove from my API.

I've tried:

    COMMENT ON CONSTRAINT users_email_unique ON public.users IS E'@omit all'; 

and:

    COMMENT ON CONSTRAINT users_email_unique ON public.users IS E'@skip'; 

... but neither of them removes the GraphQL field.

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### Additional context

It would  be super helpful if the documentation contained more examples.  Even a single (one-line) example of omiting (skipping? hiding?) *any* constraints (unique or foreign) would have been great.

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