tests: qemuxml2argv: remove some QEMU_CAPS_DEVICE problem cases

tests: qemuxml2argv: remove some QEMU_CAPS_DEVICE problem cases

When we unconditionally enable QEMU_CAPS_DEVICE, these tests need
some massaging, so do it ahead of time to not mix it in with the
big test refresh.

- minimal-s390 is not a real world working config, so drop it
- disk-usb was testing for an old code path that will be removed.
  instead use it to test lack of USB disk support, and rename it
  to disk-usb-nosupport. Switch xml2xml to use disk-usb-device for
  input.
- cputune-numatune was needlessly using q35, switch it to an older
  machine type