Removed buggy exception error handler

`set_exception_handler` expects a function that takes exception as a single argument (see http://php.net/manual/en/function.set-exception-handler.php).
Setting `handleError` as exception handler produces `PHP Fatal error:  Uncaught exception 'ErrorException' with message 'Missing argument 2 for Codeception\Subscriber\ErrorHandler::errorHandler()' in /some/path/codeception/codeception/src/Codeception/Subscriber/ErrorHandler.php:31`