What is the risk of icing with water / moisture on wings prior to takeoff?
Taking off with wet wings is not a problem, the airflow is going to blow the water off long before it reaches the freezing point. There's no concerns here. 

Given the scenario what I would be concerned about would be ice elsewhere on the airframe. 40°F (4°C) could mean that the aircraft was frozen overnight, and there could be ice left over where the sun didn't melt it off. That kind of ice wouldn't necessarily impact the airflow on the wing, but it would make the airplane heavier and therefore impact performance. A simple visual check on the walk-around will confirm this. If there is ice left then deal with it even if it's not on the wing or tail, if it's just wet then get in and fly.