cmd/tailscale/cli: hide old, useless --host-routes flag

It was from very early Tailscale and no longer makes sense.

Change-Id: I31b4e728789f26b0376ebe73aa1b4bbbb1d62607
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscale/cli/cli.go

@@ -335,6 +335,9 @@ func usageFuncOpt(c *ffcli.Command, withDefaults bool) string {
 		c.FlagSet.VisitAll(func(f *flag.Flag) {
 			var s string
 			name, usage := flag.UnquoteUsage(f)
+			if strings.HasPrefix(usage, "HIDDEN: ") {
+				return
+			}
 			if isBoolFlag(f) {
 				s = fmt.Sprintf("  --%s, --%s=false", f.Name, f.Name)
 			} else {

cmd/tailscale/cli/up.go

@@ -95,7 +95,7 @@ func newUpFlagSet(goos string, upArgs *upArgsT) *flag.FlagSet {
 	upf.StringVar(&upArgs.server, "login-server", ipn.DefaultControlURL, "base URL of control server")
 	upf.BoolVar(&upArgs.acceptRoutes, "accept-routes", acceptRouteDefault(goos), "accept routes advertised by other Tailscale nodes")
 	upf.BoolVar(&upArgs.acceptDNS, "accept-dns", true, "accept DNS configuration from the admin panel")
-	upf.BoolVar(&upArgs.singleRoutes, "host-routes", true, "install host routes to other Tailscale nodes")
+	upf.BoolVar(&upArgs.singleRoutes, "host-routes", true, "HIDDEN: install host routes to other Tailscale nodes")
 	upf.StringVar(&upArgs.exitNodeIP, "exit-node", "", "Tailscale exit node (IP or base name) for internet traffic, or empty string to not use an exit node")
 	upf.BoolVar(&upArgs.exitNodeAllowLANAccess, "exit-node-allow-lan-access", false, "Allow direct access to the local network when routing traffic via an exit node")
 	upf.BoolVar(&upArgs.shieldsUp, "shields-up", false, "don't allow incoming connections")