A new piece of glass. Unless there's etching or complicated beveling, it's almost certainly not worth your while to try to "remove" the scratch. Glass is cheap and almost always very easy to replace.

If you want to repair it, there are three theoretical options:

• Fill the scratch with a material that has the same refractive index as the glass. These tend to chip out, and different glasses have different refractive properties.
• Buff the scratch out. Unless you're willing to live with very noticeably scratched glass, you're going to spend hours polishing.
• Melt the glass. Take a blowtorch to it and you might be able to knock the sharp edges off of the scratch. I cannot imagine that this would work well at all in practice. You're far too likely to melt soot into the glass, have a nasty sag, or torch a hole through it, or all of the above, assuming you can get it to melt at all. Sounds like a fun thing to try after you've already replaced the glass, though.