Remove leftover clean_logger call in tests

[awaelchli]

What does this PR do?

Follow up to #10896

The _clean_logger method was removed in #10896 and the test here was still using it, not failing of course because who would expect a test to fail due to AttributeError, right?

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Did you have fun?

I made sure I had fun coding 🙃

Part of #1 (it's a lie, this is just here to avoid noisy GitHub bot)

cc @justusschock @awaelchli @akihironitta @Borda