I don't know if they removed it, but it should be at the bottom, but if the payment was made with steam money you can't refund in a different payment method
Let's see, from what I know, if you use your credit card and buy a $25 card and buy a game you can't refund it to your credit card, but if you paid the game directly with your card then you can choose between payment method
Works normal, if you pay from wallet you only have the option to back money to the wallet if you pay PAYPAL or CARD you have the option to back money to CARD. Example My last buy Deus EX I have chosen PAYPAL or Wallet