tails-persistence-setup check for persistence in use applies even when acting on a different device

After changing the polkit settings to allow creation of persistent volumes on non-tails usb devices (in this case /dev/sdc), I would expect to also be able to use the `delete` step to wipe the persistent partition as well. Instead, users see this:

Error

Cannot delete the persistent volume while in use. You should restart Tails without persistence.

Alternatively, I would perhaps expect the `—force` flag to bypass the check, but the same error results.

This is the command used (after editting the polkit file):

tails-persistence-setup --force --steps delete --override-boot-device /org/freedesktop/UDisks/devices/sdc

Thanks!

Related issues

• Blocks #6621

Original created by @patcon on 8935 (Redmine)