isabus-bridge: Remove user_creatable flag

isabus-bridge needs to be created by isa_bus_new(), and won't
work with -device, as it won't create the TYPE_ISA_BUS bus
itself. Remove the user_creatable flag from the device class.

Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Acked-by: Marcel Apfelbaum <marcel@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170503203604.31462-13-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

hw/isa/isa-bus.c

@@ -221,11 +221,6 @@ static void isabus_bridge_class_init(ObjectClass *klass, void *data)
 
     set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories);
     dc->fw_name = "isa";
-    /*
-     * FIXME: Set only because we are not sure yet if this device
-     * will be outside the q35 sysbus whitelist.
-     */
-    dc->user_creatable = true;
 }
 
 static const TypeInfo isabus_bridge_info = {