output/raop: delete the RAOP plugin

This plugin is horrible code, I mean it.  Last year, I tried hard to
fix it, but I figured would take less time to do a full rewrite.
Given that I don't even have any device that supports RAOP, I can't do
that properly.  After 16 months, nobody volunteered for fixing it.
Hereby, I delete it, because having no RAOP plugin is better than
having this mess.  Sorry.

src/output/raop_output_plugin.h

@@ -1,37 +0,0 @@
-/*
- * Copyright (C) 2003-2011 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.
- */
-
-#ifndef MPD_RAOP_OUTPUT_PLUGIN_H
-#define MPD_RAOP_OUTPUT_PLUGIN_H
-
-#include <glib.h>
-
-#include <stdbool.h>
-
-struct raop_data;
-
-extern const struct audio_output_plugin raop_output_plugin;
-
-bool
-raop_set_volume(struct raop_data *rd, unsigned volume, GError **error_r);
-
-int
-raop_get_volume(struct raop_data *rd);
-
-#endif