Handle default system connection transfer properly on machine removal

[jakecorrenti]

Changes system connection removal so the following case now works as expected:

• Rootless podman machine 1 is initialized and running.
• Rootful podman machine 2 is initialized.
• Delete podman machine 1.
• The rootful system connection associated with podman machine 2 now becomes the default, not the rootless.

Fixes: #22577

Does this PR introduce a user-facing change?

When a user has a rootless machine running and another rootful podman machine initialized, and the rootless machine is removed, the rootful system connection associated with the podman machine now becomes the default as expected.