[media] cec/TODO: drop comment about sphinx documentation

The CEC documentation has been converted to sphinx, so this
TODO item can be dropped.
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/staging/media/cec/TODO

@@ -14,7 +14,6 @@ Other TODOs:
 
 - Add a flag to inhibit passing CEC RC messages to the rc subsystem.
   Applications should be able to choose this when calling S_LOG_ADDRS.
-- Convert cec.txt to sphinx.
 - If the reply field of cec_msg is set then when the reply arrives it
   is only sent to the filehandle that transmitted the original message
   and not to any followers. Should this behavior change or perhaps