I wouldn't myself just to spare my friend the pain and stress. And what if he has a different opinion on what should happen? Don't want to deal with that drama when it is already a very difficult situation to be in.
If I were the guy, I would want to know, so I would tell. Even if it was a one night stand, the man should know what you intend to do with what would be his future offspring.
It's a little different because they were in a relationship, but that is why SO left his ex-wife. Not because she had an abortion 25 years ago (his baby) but because she didn't ever tell him. He was going through old medical records before their move and he found some documents from the abortion clinic she went to. He was heartbroken.