ipn: remove unused Notify.BackendLogID

Updates #14129

Change-Id: I13b5df8765e786a4a919d6b2e72afe987000b2d1
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/backend.go

@@ -100,7 +100,6 @@ type Notify struct {
 	NetMap        *netmap.NetworkMap // if non-nil, the new or current netmap
 	Engine        *EngineStatus      // if non-nil, the new or current wireguard stats
 	BrowseToURL   *string            // if non-nil, UI should open a browser right now
-	BackendLogID  *string            // if non-nil, the public logtail ID used by backend
 
 	// FilesWaiting if non-nil means that files are buffered in
 	// the Tailscale daemon and ready for local transfer to the
@@ -173,9 +172,6 @@ func (n Notify) String() string {
 	if n.BrowseToURL != nil {
 		sb.WriteString("URL=<...> ")
 	}
-	if n.BackendLogID != nil {
-		sb.WriteString("BackendLogID ")
-	}
 	if n.FilesWaiting != nil {
 		sb.WriteString("FilesWaiting ")
 	}

ipn/ipnlocal/local.go

@@ -2157,10 +2157,7 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 
 	blid := b.backendLogID.String()
 	b.logf("Backend: logs: be:%v fe:%v", blid, opts.FrontendLogID)
-	b.sendToLocked(ipn.Notify{
-		BackendLogID: &blid,
-		Prefs:        &prefs,
-	}, allClients)
+	b.sendToLocked(ipn.Notify{Prefs: &prefs}, allClients)
 
 	if !loggedOut && (b.hasNodeKeyLocked() || confWantRunning) {
 		// If we know that we're either logged in or meant to be