Function delete 

pub async fn delete(
    root: &Path,
    ancestor_cap: usize,
    namespace: &str,
    collection: &str,
    id: &str,
    expected: Option<Revision>,
) -> Result<DeleteOutcome>

Delete one record by writing a tombstone attributed to CLI_AUTHOR (spec §3.1–§3.2). Deleting an absent or already-deleted key is Deleted.