Show how @parameterized could replace @data_provider

[lizard-boy]

Summary

@data_provider seems unnecessary to include in libcst. Why not use a pypi equivalent. Here is an example using parameterized

Let me know what you think and I'll convert the rest of the tests

Test Plan

(libcstvenv) lpetre@lpetre-mbp LibCST % python -m unittest libcst._nodes.tests.test_assert
..........
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Ran 10 tests in 0.080s

OK