net/dns: remove Cleanup manager parameter.

It's only use to skip some optional initialization during cleanup,
but that work is very minor anyway, and about to change drastically.

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

net/dns/config.go

@@ -63,7 +63,4 @@ type ManagerConfig struct {
 	Logf logger.Logf
 	// InterfaceName is the name of the interface with which DNS settings should be associated.
 	InterfaceName string
-	// Cleanup indicates that the manager is created for cleanup only.
-	// A no-op manager will be instantiated if the system needs no cleanup.
-	Cleanup bool
 }

net/dns/manager.go

@@ -94,7 +94,6 @@ func Cleanup(logf logger.Logf, interfaceName string) {
 	mconfig := ManagerConfig{
 		Logf:          logf,
 		InterfaceName: interfaceName,
-		Cleanup:       true,
 	}
 	dns := NewManager(mconfig)
 	if err := dns.Down(); err != nil {

net/dns/manager_linux.go

@@ -7,17 +7,9 @@ package dns
 func newManager(mconfig ManagerConfig) managerImpl {
 	switch {
 	case isResolvedActive():
-		if mconfig.Cleanup {
-			return newNoopManager(mconfig)
-		} else {
-			return newResolvedManager(mconfig)
-		}
+		return newResolvedManager(mconfig)
 	case isNMActive():
-		if mconfig.Cleanup {
-			return newNoopManager(mconfig)
-		} else {
-			return newNMManager(mconfig)
-		}
+		return newNMManager(mconfig)
 	case isResolvconfActive():
 		return newResolvconfManager(mconfig)
 	default:

net/dns/noop.go

@@ -1,17 +0,0 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package dns
-
-type noopManager struct{}
-
-// Up implements managerImpl.
-func (m noopManager) Up(Config) error { return nil }
-
-// Down implements managerImpl.
-func (m noopManager) Down() error { return nil }
-
-func newNoopManager(mconfig ManagerConfig) managerImpl {
-	return noopManager{}
-}