Not necessarily directed at OP, but how you need to UNroot your device can depend on what the current software version is, as well as what method was used to root in the first place, but I'd imagine that you would want to investigate first.
FYI, the "auto root" method you speak from back in the day did in fact use ADB, the commands were just put into a script for more user-friendliness. Ah...memories....