Test cleanup for completion/duration tests

It'd be good to place this outside of the describe('getCompletionCriteriaLabels') block, because it doesn't test, neither describe behavior of getCompletionCriteriaLabels function like other tests cases but rather that of getCompletionDataFromNode. This applies to another new test case below as well.

A nice way to try out if tests organizations and descriptions make sense from the documentation point of view is to run the test suite with --verbose flag and read through the output

yarn test-jest channelEdit/__tests__/utils.spec --verbose

And this is nitpick (squared), on the screenshot above you can also see that it may be nice to distinguish between audio and video test cases descriptions to be able to say which one corresponds to which as right now, their names are identical. If one of them failed, ideally we'd be able to say immediately if it fails for video or for audio without digging deep into the tests code.

Originally posted by @MisRob in https://github.com/learningequality/studio/pull/4182#discussion_r1251514139