Remove non-canonical tests for `pig-latin`

[jiegillet]

Closes #1491

We had some tests that are not in the canonical data, including some that seems to actually break the rules (maybe even all of them). This makes our example implementation a bit awkward, because we know it can break the rules, but I didn't change it.

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This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

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