def delete_attribute(key_name)
      key_name_sym = key_name.to_sym
      meta = ensure_metadata_exists(key_name_sym)
      @cache.delete(key_name)
      @writethrough.delete(key_name)
      @source.delete(meta.source_key)
      nil
    end
def delete_attribute(key_name)
      key_name_sym = key_name.to_sym
      meta = ensure_metadata_exists(key_name_sym)
      @cache.delete(key_name)
      @writethrough.delete(key_name)
      @source.delete(meta.source_key)
      nil
    end
Delete an attribute
 @param key_name [Symbol] the name of the key
 @return [void]