You cannot delete content on Drupal.org. I'd say just add a note to the project page saying that the project page is available, and that anyone who wants it can have it.
I have two ideas for Drupal modules a couple of years ago and immediately reserved the namespace for them at http://drupal.org/project/ariel and http://drupal.org/project/caliban.I've only just been reminded of these projects, and I now don't have the time to develop the ideas or write the code. How can I got about getting the projects removed from Drupal.org?