Removing silicone residues from glass is difficult as silicone combines with the surface molecules of the glass.
The best advice seems to use a very sharp flat blade similar to a paint scraper. There is a tool which holds razor blades or Stanley knife blades which is suitable. Keep the blade as near parallel to the glass surface as possible. Take thin slices of the silicone away at each pass. Keep the blade free from nicks. Change the blade frequently. You may be able to remove almost all the silicone, depending on the smoothness of the glass surface, in this way.
However when you have removed as much as possible by the mechanical means, you may need to use a chemical process to get rid of the remaining silicone. Silicone dissolvers are available from most do-it-yourself shops. Make sure you use them in accordance with the instructions as they can be mildly toxic.