Since getting a replacement front windscreen, I haven't been able to get water to bead on it. Water just spreads out evenly, making vision difficult. I've tried Jiff, dishwashing liquid, soap, Autosol, petrol, etc, but to no avail.
A lot depends on what caused the condition, and if it is from the wrapping plastic, either petrol or kerosene would clean it off. If that does not work, you will have to start experimenting with different solvents. Try paint thinner as that usually take off most paint-based films. Do not use Autosol or manyabrasive cleaners, as they will leave scratches on the glass.