Simplify exception logical condition

When rendering the custom exception page, we test if the
MissingRequiredAttributeException. But it also had to be a HTTP
exception. That was never the case (also before #313).

By removing the first part of the statement, the error message is
displayed correctly once again.

src/Surfnet/StepupSelfService/SelfServiceBundle/Controller/ExceptionController.php

@@ -28,7 +28,6 @@
 use Throwable;
 use Surfnet\StepupBundle\Controller\ExceptionController as BaseExceptionController;
 use Surfnet\StepupSelfService\SelfServiceBundle\Exception\MissingRequiredAttributeException;
-use Symfony\Component\HttpKernel\Exception\HttpException;
 
 final class ExceptionController extends BaseExceptionController
 {
@@ -39,7 +38,7 @@ protected function getPageTitleAndDescription(Throwable $exception): array
     {
         $translator = $this->getTranslator();
 
-        if ($exception instanceof HttpException && $exception instanceof MissingRequiredAttributeException) {
+        if ($exception instanceof MissingRequiredAttributeException) {
             $title = $translator->trans('stepup.error.missing_required_attribute.title');
             $description = $exception->getMessage();
         }