partly revert [23991]. vlc:skip ain't supported, and that

vlc:nop->vlc:skip revert was unintented.

modules/demux/playlist/xspf.c

@@ -712,7 +712,7 @@ static vlc_bool_t parse_extension_node COMPLEX_INTERFACE
             msg_Warn( p_demux, "<node> requires \"title\" attribute" );
             return VLC_FALSE;
         }
-        p_new_input = input_ItemNewWithType( VLC_OBJECT( p_playlist ), "vlc:skip",
+        p_new_input = input_ItemNewWithType( VLC_OBJECT( p_playlist ), "vlc:nop",
                                 psz_title, 0, NULL, -1, ITEM_TYPE_DIRECTORY );
         if( p_new_input )
         {