tests: qemuhotplug: Use DEVICE_DELETED event in all hotunplug tests

tests: qemuhotplug: Use DEVICE_DELETED event in all hotunplug tests

Currently all supported qemu versions now have support for the
DEVICE_DELETED event. This means that testing the old approach is a
waste of time.

Always add the QEMU_CAPS_DEVICE_DEL_EVENT capability in the hotplug test
and fix existing test cases.

The 'disk-virtio', 'disk-usb', 'disk-scsi', and 'disk-scsi-2' already
had variants that used the event, so the non-event variants will be
removed.

For all other cases the QMP_DEVICE_DELETED macro is used to add the
correct reply.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>