I think this indicates that it can indeed be safely removed from Debian? I'm CC'ing developers that have made uploads to this packages in the past for additiponal opinions as I suspect the issue is more subtle than that.
dak rm does not take account of virtual packages. So for rust packages it is generally useless. In terms of reverse dependencies, a number have already moved to the fork rustls-webpki. However there are still a few left. Specifically rust-async-tls, rust-trust-dns-proto and rust-trust-dns-client. async-tls has not switched upstream. On the other hand I don't see any packages in Debian using it yet. ccing mjt to see what the reason for packaging it was. trust-dns-proto and trust-dns-server have switched upstream, however updating the trust-dns-packages has proved a bit more involved than I would have liked. I pushed my current efforts to the branch trust-dns-0.23 in the debcargo-conf repo. The main thing left to deal with regarding the trust-dns is aardvark-dns, the code changes needed were beyond my skills, so I reported an issue upstream. Upstream has come up with a patch but has not merged it yet. https://github.com/containers/aardvark-dns/pull/381
