Cersei or the Mountain.

Scrapped the Hound and Ilyn Payne's actor had cancer or something so he was scrapped as well.

Had cancer. He’s now apparently free of it.

The Mountain is the Hound's kill, she said she took the Hound off her list, and we haven't seen Ilyn Payne in a while, but if his actor has recovered he could get a cameo and be killed by Arya on her way to going after Cersei.

One of the very few ways Cersei can possibly be defeated now is for Arya to kill her, though it might be a little repetitive after she just killed the Night King.

Or Arya could kill Payne and become him so she can kill Cersei while the hound takes on the Mountain.

That would fit. Those two are the most likely for her to kill.

Isn't cersei supposed to die by Jamie's or tyrions hand according to the witch?

It's a prophecy. The writers have fucked up everything else, don't see why they get this right

I don't remember that part of the prophecy. If so, probably Jaime, he's on his way to kill her right now, and it is most fitting.