clean up CPP includes

Try to only include headers which are really needed.  We should
particularly check all "headers including other headers".  The
long-term goal is to have a manageable, small API for plugins
(decoders, output) without so many mpd internals cluttering the
namespace.

git-svn-id: https://svn.musicpd.org/mpd/trunk@7319 09075e82-0dd4-0310-85a5-a0d7c8717e4f

src/decode.c

@@ -20,15 +20,10 @@
 
 #include "player.h"
 #include "playerData.h"
-#include "utils.h"
 #include "pcm_utils.h"
-#include "audio.h"
 #include "path.h"
 #include "log.h"
-#include "sig_handlers.h"
 #include "ls.h"
-#include "utf8.h"
-#include "os_compat.h"
 
 /* called inside decoder_task (inputPlugins) */
 void decoder_wakeup_player(void)