n_gsm: update TODO list

This is now out of date so fix it
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/tty/n_gsm.c

@@ -21,7 +21,6 @@
  *	Mostly done:	ioctls for setting modes/timing
  *	Partly done:	hooks so you can pull off frames to non tty devs
  *	Restart DLCI 0 when it closes ?
- *	Test basic encoding
  *	Improve the tx engine
  *	Resolve tx side locking by adding a queue_head and routing
  *		all control traffic via it