Remove restoring gon in tests

What does this MR do and why?

Remove restoring gon in tests afterEach blocks

This change is an addition to !114276 (merged) so we don't leave "bad examples" in the code of tests wrongly restoring window.gon to its previous states unnecessarily.

See more at: https://docs.gitlab.com/ee/development/testing_guide/frontend_testing.html#manipulate-gon-object

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NA

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