Remove deprecated content from custom domains documentation

Author: astrojuanlu

docs/custom_domains.rst

@@ -132,42 +132,3 @@ You will need to update your CAA records to allow us to issue the certificate.
    If your custom domain was previously used in GitBook, contact GitBook support (via live chat in their website)
    to remove the domain name from their DNS Zone in order for your domain name to work with Read the Docs,
    else it will always redirect to GitBook.
-
-Proxy SSL
----------
-
-.. warning::
-
-   This option is deprecated,
-   we already issue SSL certificates for all domains.
-
-If you would prefer to do your own SSL termination
-on a server you own and control,
-you can do that although the setup is a bit more complex.
-
-Broadly, the steps are:
-
-* Have a server listening on 443 that you control
-* Procure an SSL certificate for your domain and provision it
-  and the private key on your server.
-* Add a domain that you wish to point at Read the Docs
-* Enable proxying to us, with a custom ``X-RTD-SLUG`` header
-
-An example nginx configuration for pip would look like:
-
-.. code-block:: nginx
-   :emphasize-lines: 9
-
-    server {
-        server_name pip.pypa.io;
-        location / {
-            proxy_pass https://pip.readthedocs.io:443;
-            proxy_set_header Host $http_host;
-            proxy_set_header X-Forwarded-Proto https;
-            proxy_set_header X-Real-IP $remote_addr;
-            proxy_set_header X-Scheme $scheme;
-            proxy_set_header X-RTD-SLUG pip;
-            proxy_connect_timeout 10s;
-            proxy_read_timeout 20s;
-        }
-    }