minor #36428 [Form] Removed legacy check in ValidationListener (Hea…

…hDude)

This PR was merged into the 3.4 branch.

Discussion
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[Form] Removed legacy check in `ValidationListener`

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | ~
| License       | MIT
| Doc PR        | ~

A left over of #13198, should have been removed in 3.0. The tests don't use `null` anymore, no update needed here, this is just about removing dead code.

Commits
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e479e51 [Form] Removed legacy check in `ValidationListener`

src/Symfony/Component/Form/Extension/Validator/EventListener/ValidationListener.php

@@ -55,8 +55,7 @@ public function validateForm(FormEvent $event)
             foreach ($this->validator->validate($form) as $violation) {
                 // Allow the "invalid" constraint to be put onto
                 // non-synchronized forms
-                // ConstraintViolation::getConstraint() must not expect to provide a constraint as long as Symfony\Component\Validator\ExecutionContext exists (before 3.0)
-                $allowNonSynchronized = (null === $violation->getConstraint() || $violation->getConstraint() instanceof Form) && Form::NOT_SYNCHRONIZED_ERROR === $violation->getCode();
+                $allowNonSynchronized = $violation->getConstraint() instanceof Form && Form::NOT_SYNCHRONIZED_ERROR === $violation->getCode();
 
                 $this->violationMapper->mapViolation($violation, $form, $allowNonSynchronized);
             }