There is a new, hidden page. crates.io just told me:

We actually have a new mechanism we're testing out for authors to delete their own crates that I think your crate is eligible for. This does not appear anywhere in the crates.io UI yet, but you should be able to go to:

https://crates.io/crates/your-crate-name/delete

and follow the instructions there. If that doesn't work, please let me know and I can take care of it.