command: use queue_print_*()

Replaced several wrapper functions from playlist.c, and make command.c
use the queue print functions directly.

src/queue_print.h

@@ -33,6 +33,14 @@ void
 queue_print_song_info(struct client *client, const struct queue *queue,
 		      unsigned position);
 
+/**
+ * Send detailed information about a range of songs in the queue to a
+ * client.
+ *
+ * @param client the client which has requested information
+ * @param start the index of the first song (including)
+ * @param end the index of the last song (excluding)
+ */
 void
 queue_print_info(struct client *client, const struct queue *queue,
 		 unsigned start, unsigned end);