instance method delete

# File activesupport/lib/active_support/vendor/memcache-client-1.7.4/memcache.rb, line 474
  def delete(key, expiry = 0)
    raise MemCacheError, "Update of readonly cache" if @readonly
    with_server(key) do |server, cache_key|
      with_socket_management(server) do |socket|
        logger.debug { "delete #{cache_key} on #{server}" } if logger
        socket.write "delete #{cache_key} #{expiry}#{noreply}\r\n"
        break nil if @no_reply
        result = socket.gets
        raise_on_error_response! result
        result
      end
    end
  end