Update Arbitrary.ts partial

let fast-check decide which properties to remove, Doesn't change much but is easier to use as a reference point :)

Before submitting a pull request, please make sure the following is done:

[x] Fork the repository and create your branch from master. (small change, ran it though)
[x] Run npm install in the repository root.
[x] If you've fixed a bug or added code that should be tested, add tests!
[x] Ensure the test suite passes (npm test).

Note. If you find a typo in the documentation, make sure to modify the corresponding source (docs are generated).

gcanti / io-ts