Move HTTPS section from auth to admin

It fits better into administration concerns

admin.rst

@@ -87,12 +87,12 @@ This is fine in small tables, but count performance degrades in big tables due t
 
   -- Pending nginx config: Remove any prefer header which contains the word count
 
-.. _hardening_https:
+.. _https:
 
 HTTPS
 -----
 
-See the :ref:`https` section of the authentication guide.
+PostgREST aims to do one thing well: add an HTTP interface to a PostgreSQL database. To keep the code small and focused we do not implement HTTPS. Use a reverse proxy such as NGINX to add this, `here's how <https://nginx.org/en/docs/http/configuring_https_servers.html>`_. Note that some Platforms as a Service like Heroku also add SSL automatically in their load balancer.
 
 Rate Limiting
 -------------

auth.rst

@@ -295,13 +295,6 @@ The last type of critique focuses on the misuse of JWT for maintaining web sessi
 
 PostgREST uses JWT mainly for authentication and authorization purposes and encourages users to do the same. For web sessions, using cookies over HTTPS is good enough and well catered for by standard web frameworks.
 
-.. _https:
-
-HTTPS
------
-
-PostgREST aims to do one thing well: add an HTTP interface to a PostgreSQL database. To keep the code small and focused we do not implement HTTPS. Use a reverse proxy such as NGINX to add this, `here's how <https://nginx.org/en/docs/http/configuring_https_servers.html>`_. Note that some Platforms as a Service like Heroku also add SSL automatically in their load balancer.
-
 Schema Isolation
 ================