To discard all messages from a cron job, including errors, add the following to the end the job's command line:
/dev/null 2>&1
If you want to just disregard just certain messages, but allow allow others, try something like this:
2>&1 | grep -v <nop><expression>â
Replace <nop><expression>â with a string that will match messages you want ignored. That way unexpected messages (i.e. important messages) will still come through.