Ok. So you may think that this sounds stupid, crazy, or like one of those youtube hacks that doesn't work. But no joke, it really works. I've done it before.
Get a bottle of perfume (any type will work, cheap or expensive).
Spray the perfume all over the area that is covered in the sticky gluey stuff
Wipe off the sticky stuff by pressing on the glass and rubbing with a towel, paper towel, or tissue. It should come off very easily