refactor: remove dns and tun relationship, the enabled of dns module should be decided by user

dns/patch.go

@@ -1,16 +0,0 @@
-package dns
-
-import D "github.com/miekg/dns"
-
-type LocalServer struct {
-	handler handler
-}
-
-// ServeMsg implement resolver.LocalServer ResolveMsg
-func (s *LocalServer) ServeMsg(msg *D.Msg) (*D.Msg, error) {
-	return handlerWithContext(s.handler, msg)
-}
-
-func NewLocalServer(resolver *Resolver, mapper *ResolverEnhancer) *LocalServer {
-	return &LocalServer{handler: NewHandler(resolver, mapper)}
-}