robot-name: remove redundant tests

[senekor]

[no important files changed]

part of #1824

This is another case where I think it makes sense to actually keep the util function around. It produces a good error message and in combination with the body of the test function, users should have enough information.

As the comment in the diff already states, the removed tests are redundant because the type system prevents such errors anyway.

[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.

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[no important files changed]

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