Remove Bootstrap 4's Cards class name from Group Members (list)

!48856 (comment 458480586)

It looks like we have 1 more place where the card-without-border class is used https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/views/groups/group_members/index.html.haml#L85

#289805 (closed)

@ekigbo @peterhegman