glcontext: Do not check for correctness in set_required_version

glcontext: Do not check for correctness in set_required_version

There are two reasons for this:
 * First, the refactored realize code now makes sure that no
   context with unsupported version is ever created.
 * Second, this code could bump into false possitives and negatives, since
   the user is not requested, nor expected to set_required_version
   in any specific order relative to set_allowed_apis. Therefore,
   some version could be rejected or accepted based on a set of
   allowed apis that the user has not yet correctly configured.