Remove the 'X-Forwarded-Proto' line from the nginx config

[cimnine]

Related Issue: #292

New Behavior

nginx does not override X-Forwarded-Proto.

Contrast to Current Behavior

nginx does overwrite whatever header an upstream proxy has defined for X-Forwarded-Proto.

Discussion: Benefits and Drawbacks

The reason for this change is that in the default configuration nginx is only serving 'http' traffic.
So if an upstream proxy sets the 'X-Forwarded-Proto' header, because it is terminating
TLS, then nginx will overwrite it to 'http'. This will cause django to think the page
is served via 'http' and it will not create 'https://...' URLs.

Changes to the Wiki

n/a

Proposed Release Note Entry

Don't mangle with X-Forwarded-Proto header #308

Nginx will no longer set or overwrite the X-Forwarded-Proto header in the default configuration.
This was implemented, because in the default configuration it would set the header to http every time.
And this would overwrite the header of an upstream proxy which might set X-Forwarded-Proto to https, because it is terminating the TLS connection.

Double Check

• I have read the comments and followed the PR template.
• I have explained my PR according to the information in the comments.
• My PR targets the develop branch.