Function revoke 

pub async fn revoke(
    conn: &mut PgConnection,
    id: Uuid,
    created_by: Uuid,
) -> ModelResult<bool>

Withdraws a share, which get_by_id then stops resolving. Scoped to the creator, so the unguessable token is not itself authority to revoke — only to view.

false means there was no live share with that id belonging to this user.