You can use this command:
dnf list installed
it will show against each package installed from which repository it came from. Obviously it lists all packages installed, but you can use that to grep for remi or virtualbox - the names of the two you wanted to disable to see if anything got left behind and not removed.
There will be exceptions to that rule if an rpm was installed outside of dnf/yum repositories for example. For example I make my own rpm for installing pycharm community on my system, and it shows @System instead of a named repository.