Remove special case for JavaScript

[BrentBlanckaert]

The value file in JavaScript still has a temporary case that should be removed. This was to temporarily allow objects with "message" and "name".

The submissions that are being tested to account for the new behaviour should be updated (the PR that introduced this is #361, which might be helpful): all exceptions must inherit from Error.

It is possible that some example solutions in the js repo will need to be updated as well.