control/controlclient: remove unused StartLogout

Updates #cleanup

Co-authored-by: Maisem Ali <maisem@tailscale.com>
Change-Id: I9d052fdbee787f1e8c872124e4bee61c7f04d142
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f