[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/context/mod.rs

@@ -46,7 +46,6 @@ struct RequestContextInner {
     pub(crate) session_id: Uuid,
     pub(crate) protocol: Protocol,
     first_packet: chrono::DateTime<Utc>,
-    region: &'static str,
     pub(crate) span: Span,
 
     // filled in as they are discovered
@@ -94,7 +93,6 @@ impl Clone for RequestContext {
             session_id: inner.session_id,
             protocol: inner.protocol,
             first_packet: inner.first_packet,
-            region: inner.region,
             span: info_span!("background_task"),
 
             project: inner.project,
@@ -124,12 +122,7 @@ impl Clone for RequestContext {
 }
 
 impl RequestContext {
-    pub fn new(
-        session_id: Uuid,
-        conn_info: ConnectionInfo,
-        protocol: Protocol,
-        region: &'static str,
-    ) -> Self {
+    pub fn new(session_id: Uuid, conn_info: ConnectionInfo, protocol: Protocol) -> Self {
         // TODO: be careful with long lived spans
         let span = info_span!(
             "connect_request",
@@ -145,7 +138,6 @@ impl RequestContext {
             session_id,
             protocol,
             first_packet: Utc::now(),
-            region,
             span,
 
             project: None,
@@ -179,7 +171,7 @@ impl RequestContext {
         let ip = IpAddr::from([127, 0, 0, 1]);
         let addr = SocketAddr::new(ip, 5432);
         let conn_info = ConnectionInfo { addr, extra: None };
-        RequestContext::new(Uuid::now_v7(), conn_info, Protocol::Tcp, "test")
+        RequestContext::new(Uuid::now_v7(), conn_info, Protocol::Tcp)
     }
 
     pub(crate) fn console_application_name(&self) -> String {