derp/derphttp: remove ban on websockets dependency

The event bus's debug page uses websockets.

Updates #15160

Signed-off-by: David Anderson <dave@tailscale.com>

cmd/tailscaled/tailscaled.go

@@ -713,7 +713,6 @@ var tstunNew = tstun.New
 
 func tryEngine(logf logger.Logf, sys *tsd.System, name string) (onlyNetstack bool, err error) {
 	conf := wgengine.Config{
-		EventBus:      sys.Bus.Get(),
 		ListenPort:    args.port,
 		NetMon:        sys.NetMon.Get(),
 		HealthTracker: sys.HealthTracker(),