I had kingroot and I uninstalled it through kingroot uninstall option in the options menu. However, I still can't add a credit card to android pay. It says Google is unable to verify that your device or the software running on it is android compatible. I also tried deleting random folders I found with the name kingroot, I tried using ccleaner, and I tried deleting data from android pay and uninstall/reinstall android pay.
Turned out I had to re-flash firmware for it to work. Instructions for re-flashing firmware for my specific device (lg g3) were incorrect which bricked my device. Luckily I found that clicking the other action mode than the one stated did the trick and my device was un-bricked. Was a scary few hours. At the end though my lg g3 worked and all residue of kingroot was gone!