aacenc: remove TNS from the todo list

Pulses are already on the way so expect to see the list
gone in the close future.

TNS is already of sufficiently high quality to be enabled
by default (but isn't yet, so you too can help by testing!).
Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>

libavcodec/aacenc.c

@@ -27,7 +27,6 @@
 /***********************************
  *              TODOs:
  * add sane pulse detection
- * add temporal noise shaping
  ***********************************/
 
 #include "libavutil/float_dsp.h"