minor symfony#52311 [6.3] Remove unused test fixture (fancyweb)

This PR was merged into the 6.3 branch.

Discussion
----------

[6.3] Remove unused test fixture

| Q             | A
| ------------- | ---
| Branch?       | 6.3
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

Commits
-------

135baad [6.3] Remove unused test fixture

Author: fabpot

src/Symfony/Component/HttpFoundation/Tests/ParameterBagTest.php

@@ -379,15 +379,3 @@ public function testGetEnumThrowsExceptionWithInvalidValueType()
         $this->assertNull($bag->getEnum('invalid-value', FooEnum::class));
     }
 }
-
-class InputStringable
-{
-    public function __construct(private string $value)
-    {
-    }
-
-    public function __toString(): string
-    {
-        return $this->value;
-    }
-}