[proxy] review and cleanup CLI args (#12167)

I was looking at how we could expose our proxy config as toml again, and
as I was writing out the schema format, I noticed some cruft in our CLI
args that no longer seem to be in use.

The redis change is the most complex, but I am pretty sure it's sound.
Since https://github.com/neondatabase/cloud/pull/15613 cplane longer
publishes to the global redis instance.

proxy/src/serverless/mod.rs

@@ -417,12 +417,7 @@ async fn request_handler(
     if config.http_config.accept_websockets
         && framed_websockets::upgrade::is_upgrade_request(&request)
     {
-        let ctx = RequestContext::new(
-            session_id,
-            conn_info,
-            crate::metrics::Protocol::Ws,
-            &config.region,
-        );
+        let ctx = RequestContext::new(session_id, conn_info, crate::metrics::Protocol::Ws);
 
         ctx.set_user_agent(
             request
@@ -462,12 +457,7 @@ async fn request_handler(
         // Return the response so the spawned future can continue.
         Ok(response.map(|b| b.map_err(|x| match x {}).boxed()))
     } else if request.uri().path() == "/sql" && *request.method() == Method::POST {
-        let ctx = RequestContext::new(
-            session_id,
-            conn_info,
-            crate::metrics::Protocol::Http,
-            &config.region,
-        );
+        let ctx = RequestContext::new(session_id, conn_info, crate::metrics::Protocol::Http);
         let span = ctx.span();
 
         let testodrome_id = request