Function destroy 

pub async fn destroy(
    backend: &SessionBackend,
    cookie_value: Option<&str>,
    cookie_name: &str,
    path: &str,
) -> Result<String, StoreError>

Revokes the session and returns the delete-cookie header value. A store delete failure is an Err — server-side revocation is the entire point of redis mode, so a logout that silently leaves the session live must fail loudly (503) instead.