hw/s390x/s390-virtio-ccw: Remove the deprecated 2.4 and 2.5 machine types

hw/s390x/s390-virtio-ccw: Remove the deprecated 2.4 and 2.5 machine types

They are older than 6 years, so according to our machine support
policy, they can be removed now.

This removes the requirements for the storage keys "migration-enabled"
property which will be removed in the next patch. It also removes
the code that sets "max_revision" to 0 for some CCW devices, but the
relating code in virtio-ccw.c indicates that 0 could have also been in
use for other machines types < 5.1, so further clean-up for code related
to "max_revision" won't be done yet (see also commit d55f518248f -
"virtio: skip legacy support check on machine types less than 5.1").

Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Message-ID: <20250103144232.520383-2-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>