The light serves a function (telling you your Mac is charging) and isn't so powerful that it's distracting so I'm really wondering why you'd want to do this.
Anyway, the signal that triggers the light is 100% hardware so you won't find some kind of Mac app that turns the light off if that's what you're looking for.
Your best solution would be to break with a needle or anything sharp (make sure it's disconnected beforehand) or putting a tape over it.
Of course! Break it, and anything else you don't like.