podman: remove subuid/subgid creation from sysext

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

Adding subuid/subgid could be done through Ignition:
```yaml
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

Author: invis-z

build_library/sysext_mangle_flatcar-podman

@@ -13,8 +13,6 @@ cp -a ./etc/{fuse.conf,containers} ./usr/share/podman/etc/
 cat <<EOF >>./usr/lib/tmpfiles.d/podman.conf
 C /etc/containers - - - - /usr/share/podman/etc/containers
 C /etc/fuse.conf - - - - /usr/share/podman/etc/fuse.conf
-w /etc/subuid - - - - core:1065536:65536
-w /etc/subgid - - - - core:1065536:65536
 EOF
 
 popd