do not store commands list in MPD::Connection

it should have sent commandlist begin and end commands from the beginning,
having separated functions just to handle queueing commands was plainly ugly.

src/libmpdclient.h

@@ -673,7 +673,7 @@ void mpd_sendPlaylistMoveCommand(mpd_Connection *connection,
                                  char *playlist, int from, int to);
 
 void mpd_sendPlaylistDeleteCommand(mpd_Connection *connection,
-                                   char *playlist, int pos);
+                                   const char *playlist, int pos);
 #ifdef __cplusplus
 }
 #endif