[Sets] Drop PHPUnitSetProvider from the collector

[TomasVotruba]

Companion to rectorphp/rector-phpunit#758, same shape as #8292 for Symfony.

That PR moves every per-version rule into composer-based.php, each bound to the phpunit/phpunit version its target API is available from, so no ComposerTriggeredSet is left in the package. What PHPUnitSetProvider still listed were three plain sets, all reachable through PHPUnitSetList::COMPOSER_BASED, PHPUNIT_CODE_QUALITY and ANNOTATIONS_TO_ATTRIBUTES.

-use Rector\PHPUnit\Set\SetProvider\PHPUnitSetProvider;
 use Rector\Set\Contract\SetInterface;

         $setProviders = [
             new PHPSetProvider(),
             new CoreSetProvider(),
-            new PHPUnitSetProvider(),
             new DoctrineSetProvider(),
             new TwigSetProvider(),
         ];

No behavior change for withComposerBased(phpunit: true) — it adds PHPUnitSetList::COMPOSER_BASED directly and never routes through SetGroup::PHPUNIT.

Merge this before rectorphp/rector-phpunit#758, which deletes the class. The reverse order leaves main instantiating a class that no longer exists.

tests/Set green: 12 tests, 15 assertions.