playlist_control: "previous" really plays the previous song

No more CD player emulation.  The current behaviour of "previous" is
difficult for a client to predict, because it does not definitely know
the current position within the song.  If a client wants to restart
the current song, it can always send "playid".

src/playlist.c

@@ -62,16 +62,12 @@ playlist_init(struct playlist *playlist)
 
 	playlist->queued = -1;
 	playlist->current = -1;
-
-	playlist->prev_elapsed = g_timer_new();
 }
 
 void
 playlist_finish(struct playlist *playlist)
 {
 	queue_finish(&playlist->queue);
-
-	g_timer_destroy(playlist->prev_elapsed);
 }
 
 /**