hw/s390x/css-bridge: Remove the "css_dev_path" property

hw/s390x/css-bridge: Remove the "css_dev_path" property

Now that the s390-ccw-virtio-2.6 and older machine types have been
removed, the "css_dev_path" property of the css-bridge is also not
used anymore and thus can be removed.

This way we finally get rid of the problem that has been described
in: https://gitlab.com/qemu-project/qemu/-/issues/2213

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Message-ID: <20250103144232.520383-7-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>