remove post-time64 unstable overrides for debian-testing image

[allisonkarlitskaya]

          Let's make sure we don't forget to take these out.

Originally posted by @allisonkarlitskaya in #6341 (comment)

[martinpitt]

Check these for re-entering testing:

• https://tracker.debian.org/pkg/virt-manager
• https://tracker.debian.org/pkg/sssd
• https://tracker.debian.org/pkg/freeipa

[mvollmer]

@martinpitt, can we do this now? What exactly should re-enter testing? Specific versions, or the package as a whole?

[martinpitt]

virt-manager and sssd are back in testing. I already re-enabled virt-install earlier, but sssd packages and corresponding cockpit tests can be re-enabled.