Clear extra updates array to prevent memory leak

[X-Coder264]

Subject

I am targeting this branch, because this is a bug fix. The extraUpdates array property is never being cleared so this results in memory leaks in long running processes (like Symfony Messenger queues) - now it's gonna be cleared on every $entityManager->clear() call.

Changelog

### Fixed
- Clear extra updates array to prevent memory leak

[VincentLanglet]

Thanks