hw/s390x/ccw: Remove deprecated s390-ccw-virtio-4.2 machine

hw/s390x/ccw: Remove deprecated s390-ccw-virtio-4.2 machine

This machine has been supported for a period of more than 6 years.
According to our versioned machine support policy (see commit
ce80c4fa6ff "docs: document special exception for machine type
deprecation & removal") it can now be removed.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20251020094903.72182-2-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>