Remove ValidationError FIXME in individual_results_validator

[dunkOnIT]

Now that #3254 is closed, we can consider making the change suggested by the FIXME in individual_results_validator:245 - @viroulep could you confirm whether or not the error in question can occur independently of the cumulative time limit bug in #3254?

In #4065 you said the following:

No: it's a situation that can occur with a "normal" error. Eg: you plan to have 444bf and 555bf with a cumulative time limit, but you end up having no results for one of the events. Until you edit the events, you can still end up in this situation.

That was the same day as the comment in #3254, so not sure which one is correct

[viroulep]

I'm actually not sure, I think it may still happen if you do have a cumulative across events, and one of them is not present in the results. Technically the error would be removed in another way in that case: an error about missing results for an event would be emitted, and when going to the edit events page to remove the event the cumulative time limit would be updated as well, thus removing the error.

It doesn't harm to keep the validation in my opinion, although it's very likely it cannot be triggered without having to trigger another error.

[dunkOnIT]

Ok great, thanks! I think the path forward is to leave it in the code as you suggest - for any contributors, we're still open to removing it - we'd want to write tests that should replicate the error exactly, and observe whether the correct error is generated before taking steps to remove it.