This change reverts part of the previous commit, and basically applies the
following logic:

- We will not do anything special because we are proxied in terms of the
headers or changing Django's perceived host. We instead rely on the proxy (e.g.
Apache) to do the rewriting as appropriate (e.g. ProxyPassReverse).

- We will make a request directly to splunkweb, adding in the remote user header
to have us authenticated using SSO. Note that this requires the local server to
be in Splunkweb's trusted IP list.