My favorite is finding the libraries that now have typings (they migrated to TS themselves or got a good definition PR they accepted, maybe even a PR you sent the library directly), and sending the removal PR to DT. DT is huge so every file that can be removed is a little bit less of a papercut in checkout time and testing time for the next branch/developer.

and please break the codebase of people using these types by not following semver (keeps happening to me with typings -_- should really start using a lock file)