Selecting a zero event price should remove billing block

Configure an event with two fees, one of them being zero.

Use case:
"Would you like us to provide you with a lunch?" $10
"I will bring my own lunch" $0

When selecting a zero price option, the billing block remains and asks for credit card.

Example: http://d46.demo.civicrm.org/civicrm/event/register?reset=1&id=12&cid=0