When user is removed from the Team and all the groups, mentioning that user by @ username still brings them up and labels as a teammate

Steps to reproduce:

1. Create a Team account
2. Create a group on the team account
3. Add a user to one of the groups with you
4. Create a repo and make one commit - even creating a Readme file in the UI works
5. Go that that commit on the repo and mention the user you added by using a @ username
6. go to the team Settings -> find that group and remove this user from the group, then review all other groups to make sure he is not lingering anywhere
7. Go back to the same commit and mention that same user you just removed by @ username -> the user will comeup and will show up as a Teammate on the label next to him

Desired behavior: after removing a user from all the group -> the user shouldn't come up on Commits or pull requests on that team when mentioning by @ username, because he is no longer a member