Get rid of legacy version

Move the logic for the legacy version into the http handlers and use a
shim when doing ipc.

common/messages/ipc.go

@@ -7,12 +7,9 @@ import (
 type Arg struct {
 	Body       []byte
 	RemoteAddr string
-	NatType    string
 }
 
 var (
-	ErrBadRequest  = errors.New("bad request")
-	ErrInternal    = errors.New("internal error")
-	ErrUnavailable = errors.New("service unavailable")
-	ErrTimeout     = errors.New("timeout")
+	ErrBadRequest = errors.New("bad request")
+	ErrInternal   = errors.New("internal error")
 )