Glance uses http-proxy-to-wsgi middleware from oslo.middleware in
its pipeline in order to efficiently forward request headers in case
of load balancer style deployments. Hence, the configuration option
``secure_proxy_ssl_header`` was marked as deprecated.
This patch removes the option and the support for it within Glance
to entirely rely on oslo middleware. This will ensure that the related
headers set by oslo.middleware:HTTPProxyToWSGI is never modified in
Glance.
Change-Id: I11d41bb736bbfd90030d88245c11642823e4c400
Closes-Bug: 1673908
8140abe639