When constructing an object listing from container shards, the proxy
would previously return the X-Backend-Record-Type header with the
value 'shard' that is returned with the initial GET response from the
root container. It didn't break anything but was plainly wrong.
This patch removes the header from object listing responses to request
that did not have the header. The header value is not set to 'object'
because in a request that value specifically means 'do not recurse
into shards'.
Change-Id: I94c68e5d5625bc8b3d9cd9baa17a33bb35a7f82f
71ad062bc3