tailcfg: remove v6-overlay debug option.
It's about to become a no-op in control.
@@ -531,8 +531,6 @@ type MapRequest struct {
// Current DebugFlags values are:
// * "warn-ip-forwarding-off": client is trying to be a subnet
// router but their IP forwarding is broken.
- // * "v6-overlay": IPv6 development flag to have control send
- // v6 node addrs
// * "minimize-netmap": have control minimize the netmap, removing
// peers that are unreachable per ACLS.
DebugFlags []string `json:",omitempty"`
