Symfony starts always a session on legacy_mode

After applying the fix from EZP-23176 lazy sessions still don't work as they should on legacy_mode.
Sessions are always created.
If we disable the legacy_mode everything works as expected, and sessions are not created, taking the lazy sessions into consideration.

Steps to reproduce:

1. Configure the lazy sessions
2. Apply fix from EZP-23176
3. Enable legacy_mode for the frontend siteaccesses
4. Access the frontend

Sessions will always be generated, and it shouldn't.