If you go to your account settings in the new Google AdSense console, known as version 3, you won't be able to remove those listed as "Users with sign-in access."
The issue was reported back in early November at the Google AdSense Help forums. It may have been reported even earlier.
Google recently responded to the thread. AdSensePro Annie said:
Thanks for your patience. We are aware of this issue and are working on it as fast as we can.
It seems like just one of those features they did not get to yet. It sounds like it is on the todo list and they will get to it soon.
This does seem to be a huge issue for many folks, so I don't know why it is taking so long to tackle.
Forum discussion at Google AdSense Help.
