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

The reason 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.

Related to #292

.gitignore

@@ -2,3 +2,4 @@
 .netbox
 .initializers
 docker-compose.override.yml
+*.pem

docker/nginx.conf

@@ -29,7 +29,6 @@ http {
             proxy_pass http://netbox:8001;
             proxy_set_header X-Forwarded-Host $http_host;
             proxy_set_header X-Real-IP $remote_addr;
-            proxy_set_header X-Forwarded-Proto $scheme;
             add_header P3P 'CP="ALL DSP COR PSAa PSDa OUR NOR ONL UNI COM NAV"';
         }
     }