fix: remove deprecated eraseCredentials() — breaks logout on Symfony 8

[smbpunt]

Summary

• Remove empty eraseCredentials() method from CasUser
• Remove $security->getToken()?->eraseCredentials() call from Logout controller
• Remove now-unused Security dependency from Logout controller

Context

eraseCredentials() was deprecated in Symfony 7.3 and removed in 8.0. Since cas-bundle now supports Symfony 8 ("symfony/framework-bundle": "^7 || ^8"), the call in the Logout controller causes a fatal error, breaking logout entirely.

Ref: https://symfony.com/blog/new-in-symfony-7-3-security-improvements#deprecate-erasecredentials-method

[smbpunt]

Heads up — compatibility concern with this PR as-is.

Removing eraseCredentials() from the Logout controller fixes the SF8 fatal error, but removing it from CasUser breaks Symfony 7.x: UserInterface still declares eraseCredentials() in all 7.x versions (deprecated in 7.3, only removed from the interface in 8.0). Since composer.json declares "^7 || ^8", this would cause a fatal error for all SF7 users.

How would you like to handle this @drupol ? Should I adjust the PR, or do you prefer a different approach?