Just redirect stdout / stderr to the bit bucket so that the emails aren't sent at all. Something like this should work. See crontab(5) for more information (man 5 crontab).
Basically, you want something like this:
* * * * * /your/cron/job >/dev/null 2>&1
If you want to receive stderr, but not stdout, just do:
* * * * * /your/cron/job >/dev/null
A quick and dirty way to accomplish what you're trying to do would be to put: