Summary
If you can't delete a media file, it's likely attached to an application.
If Something Goes Wrong
Symptom: You see "This media is currently in use" when trying to delete a file.
Cause: The file is attached to an application. Files attached to a submitted application can't be deleted.
Fix: If the file is on an in-progress, unsubmitted application, remove it from the application first, then delete it.