Remove choosePort and rely on dynamic, OS-allocated ports during tests

[Ewen Cheslack-Postava (ewencp)]

No description provided.

[Ewen Cheslack-Postava (ewencp)]

Works in conjunction with confluentinc/rest-utils#90 and avoids Address already in use errors during tests due to choosePort not being a reliable way to select a random available port.

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