podman: remove subuid/subgid creation from sysext

[invis-z]

Following what was done for incus in #3028 . Removes the subuid/gid from sysext.

Adding subuid/subgid could be done through Ignition:

version: 1.1.0
variant: flatcar
storage:
  files:
    - path: /etc/subuid
      append:
        - inline: |
            core:1065536:65536
    - path: /etc/subgid
      append:
        - inline: |
            core:1065536:65536

Related: flatcar/Flatcar#1733

• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)
• Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.

[doraskayo]

Hi. I'm trying to add users to /etc/sub{u,g}id but it looks like the podman sysext overwrites my changes.

It would be great to get this merged fairly soon.

[tormath1]

Thanks @invis-z for your contribution and sorry for the delay here, the PR is approved and I will merge it right now. As it can be breaking for some users, I will not yet backport it to maintenance channels. I don't expect it to break existing workloads as the shipped subuid/subgid will stay in place inside /etc but new deployed instances will not have this settings so it has to be added manually to the initial provisioning so this can break new deployments.

[github-actions]

Build action triggered: https://github.com/flatcar/scripts/actions/runs/16517073597