hw/pc_piix: remove is_default for pc-0.15

Signed-off-by: NJordan Justen <jordan.l.justen@intel.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/pc_piix.c

@@ -385,7 +385,6 @@ static QEMUMachine pc_machine_v0_15 = {
     .desc = "Standard PC",
     .init = pc_init_pci,
     .max_cpus = 255,
-    .is_default = 1,
 };
 
 static QEMUMachine pc_machine_v0_14 = {