httpreplay: ignore Connection header
httpreplay: ignore Connection header

Connection is a standard header that is not relevant
to the semantics of the request.

It confuses replay when using a Python client.

Change-Id: I616dac39c6e5748b6e907f39ba434b7c53e77e0e
Reviewed-on: https://code-review.googlesource.com/30070
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Jean de Klerk <605b93664484fed1e671a07bff68da39e73d0174@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go