My advice would be to change the whois to bogus information, and then delete the domain if it is at godaddy.
If it's not (other registrars don't offer this option AIUI), turn off autorenew so that when it does come renewal time, it will expire.
And for the time being, forward the site to google.com, or something innocuous that won't let them apply the argument that your website is displaying competing wares, which it likely is, if it's being forwarded to a parked page.
For example, if you owned Apple.com, Apple couldn't come after you if you were selling something that had nothing to do with computers or any of their wares, but if it resolved to a parked page which displayed ads for PC manufacturers such as Dell and HP, you'd be asking for trouble.