Running Sierra 10.12.6 without administrator privileges, the system has some problem with my iCloud profile. Whenever accessing anything remotely related to it, the respective app beachballs indefinitely. This includes the Preferences pane, so I could not even delete my account from there. I managed to find the necessary Terminal command:
defaults delete MobileMeAccounts
It worked, almost. Even without root access/
sudo, this indeed reset the iCloud pane in Preferences, but it did not remove the iCloud and Game Center entries from the Internet Accounts pane. They are merely listed as inactive or disabled (I'm not using the English locale). If I select either of them, Preferences still beachballs, of course.
How can I permanently remove those accounts using the Terminal, probably using
For what it's worth, this did not do the trick:
defaults delete com.apple.gamecenter
PS: If you want to suggest solutions to the underlying iCloud problem, please use comments instead of answers.