Remove gen-test script

[alice-i-cecile]

Objective

Initial progress towards #133. We do not intend to fix this script, so it's better to remove it proactively.

See discussion in the linked issue for why these generated tests suck.

[mockersf]

I really don't think this is a good idea, and it pretty much removes any trust that I would have in evolutions of this library

[TimJentzsch]

@mockersf Do you have ideas to make the generated tests easier to maintain?
Currently, they are definitely a big maintenance burden, especially for refactorings.

Maybe one solution would be to not commit them to the repository and generate them "fresh" in CI?
But I'm not sure how much time and resources that would need.

[alice-i-cecile]

The gen-tests script itself is very broken, and currently does nothing. Removing this folder in this PR has no effect other than to clarify this state to contributors and remove unactionable errors in IDEs.

If we decide to take an alternative path in #133, we can revert this change and tackle a cleanup.

I want to synchronize with Chrome still, but I think that this code generation approach is unmaintainable.