hw/virtio: Remove VirtIOBalloon::qemu_4_0_config_size field

The VirtIOBalloon::qemu_4_0_config_size boolean was only set in
the hw_compat_4_0[] array, via the 'qemu-4-0-config-size=true'
property.  We removed all machines using that array, lets remove
that property.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20260307154202.86309-6-philmd@linaro.org>

hw/virtio/virtio-balloon.c

@@ -708,9 +708,6 @@ static size_t virtio_balloon_config_size(VirtIOBalloon *s)
 {
     uint64_t features = s->host_features;
 
-    if (s->qemu_4_0_config_size) {
-        return sizeof(struct virtio_balloon_config);
-    }
     if (virtio_has_feature(features, VIRTIO_BALLOON_F_PAGE_POISON)) {
         return sizeof(struct virtio_balloon_config);
     }
@@ -1054,8 +1051,6 @@ static const Property virtio_balloon_properties[] = {
      * is disabled, resulting in QEMU 3.1 migration incompatibility.  This
      * property retains this quirk for QEMU 4.1 machine types.
      */
-    DEFINE_PROP_BOOL("qemu-4-0-config-size", VirtIOBalloon,
-                     qemu_4_0_config_size, false),
     DEFINE_PROP_LINK("iothread", VirtIOBalloon, iothread, TYPE_IOTHREAD,
                      IOThread *),
 };

include/hw/virtio/virtio-balloon.h

@@ -70,7 +70,6 @@ struct VirtIOBalloon {
     int64_t stats_poll_interval;
     uint32_t host_features;
 
-    bool qemu_4_0_config_size;
     uint32_t poison_val;
 
     /* State of the resettable container */