Pervasive Kingroot app avoids uninstall
You did it wrong I guess. Despite all the tutorials you found online, I wonder how you missed the right one : There's a "safe" uninstall feature within Kingoroot app. This removes completely the app and the binaries from your device. 


Open the app
Click three dots upper right, find settings menu.
Click "Remove Root".


Your device will be rebooted and root should be removed.