unimplemented-device: Remove user_creatable flag

unimplemented-device needs to be created and mapped using
create_unimplemented_device() (or equivalent code), and won't
work with -device. Remove the user_creatable flag from the device
class.

Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: Marcel Apfelbaum <marcel@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170503203604.31462-14-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

hw/misc/unimp.c

@@ -90,11 +90,6 @@ static void unimp_class_init(ObjectClass *klass, void *data)
 
     dc->realize = unimp_realize;
     dc->props = unimp_properties;
-    /*
-     * 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 unimp_info = {