Assistant: ifdef qWarning about missing translations

There's no reason for only assistant to do this, and there are enough
missing translations that a lot of users will tend to see this message.

Task-number: QTBUG-31747
Change-Id: I333d15eaeb603e4c64a1a12791b4f94658b80e80
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>