Remove nodisk_ok machine feature (Jan Kiszka)

Remove nodisk_ok machine feature (Jan Kiszka)

All archs have some kind of firmware to load and can be fine with it
already. So there is not much use in enforcing the presence of a disk.
If the system setup requires one, the user will notice it anyway once
the firmware/bios fails to boot from it.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6899 c046a42c-6fe2-441c-8c8c-71466251a162