Revert "cmd/tailscaled, ipn/{ipnlocal,ipnserver}: let netstack get access to LocalBackend"

This reverts commit 2bc518dcb2.

@namansood didn't end up needing it in his 770aa71ffb.

cmd/tailscaled/tailscaled.go

@@ -29,7 +29,6 @@ import (
 	"time"
 
 	"github.com/go-multierror/multierror"
-	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/ipn/ipnserver"
 	"tailscale.com/logpolicy"
 	"tailscale.com/net/socks5"
@@ -228,8 +227,6 @@ func run() error {
 		return err
 	}
 
-	localBEFuture := ipnlocal.NewLocalBackendFuture()
-
 	var ns *netstack.Impl
 	if useNetstack {
 		tunDev, magicConn := e.(wgengine.InternalsGetter).GetInternals()
@@ -301,7 +298,6 @@ func run() error {
 		LegacyConfigPath:   paths.LegacyConfigPath(),
 		SurviveDisconnects: true,
 		DebugMux:           debugMux,
-		OnBackendCreated:   localBEFuture.Set,
 	}
 	err = ipnserver.Run(ctx, logf, pol.PublicID.String(), ipnserver.FixedEngine(e), opts)
 	// Cancelation is not an error: it is the only way to stop ipnserver.