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.

[github-actions]

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[github-actions]

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.

If this PR does not affect the result of the test (or, for example, adds an edge case that is not worth rerunning all tests for), please add the following to the merge-commit message which will stops student's tests from re-running. Please copy-paste to avoid typos.

[no important files changed]

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