net/dns: remove ManagerConfig, pass relevant args directly.

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

net/dns/direct.go

@@ -110,7 +110,7 @@ func isResolvedRunning() bool {
 // or as cleanup if the program terminates unexpectedly.
 type directManager struct{}
 
-func newDirectManager(mconfig ManagerConfig) managerImpl {
+func newDirectManager() managerImpl {
 	return directManager{}
 }