Project Group Role is not removed when the Project Group has been deleted.

Steps to reproduce.

1. Create a Project Group.
2. Create a user
3. Edit role of the new created user and assign it as a Project Administrator of the Project Group created in step 1.
4. Go back to group summary page and delete project group.
5. Check the role of user created in step 3. Role is not deleted or assigned.

Roles for the project group that was deleted can still be seen in the role list page.
Roles also can be seen when creating or creating a user even though project group has been removed.