protocol/Ack: remove unused variable `ack_domain`

meson.build

@@ -224,7 +224,6 @@ log_dep = declare_dependency(
 sources = [
   version_cxx,
   'src/Main.cxx',
-  'src/protocol/Ack.cxx',
   'src/protocol/ArgParser.cxx',
   'src/protocol/Result.cxx',
   'src/command/CommandError.cxx',

src/protocol/Ack.cxx

@@ -1,23 +0,0 @@
-/*
- * Copyright 2003-2020 The Music Player Daemon Project
- * http://www.musicpd.org
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along
- * with this program; if not, write to the Free Software Foundation, Inc.,
- * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
- */
-
-#include "Ack.hxx"
-#include "util/Domain.hxx"
-
-const Domain ack_domain("ack");

src/protocol/Ack.hxx

@@ -25,8 +25,6 @@
 #include <stdexcept>
 #include <utility>
 
-class Domain;
-
 enum ack {
 	ACK_ERROR_NOT_LIST = 1,
 	ACK_ERROR_ARG = 2,
@@ -43,8 +41,6 @@ enum ack {
 	ACK_ERROR_EXIST = 56,
 };
 
-extern const Domain ack_domain;
-
 class ProtocolError : public std::runtime_error {
 	enum ack code;
 

test/meson.build

@@ -264,7 +264,6 @@ if enable_database
   executable(
     'DumpDatabase',
     'DumpDatabase.cxx',
-    '../src/protocol/Ack.cxx',
     '../src/db/Registry.cxx',
     '../src/db/Selection.cxx',
     '../src/db/PlaylistVector.cxx',