[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/config.rs

@@ -22,7 +22,6 @@ pub struct ProxyConfig {
     pub http_config: HttpConfig,
     pub authentication_config: AuthenticationConfig,
     pub proxy_protocol_v2: ProxyProtocolV2,
-    pub region: String,
     pub handshake_timeout: Duration,
     pub wake_compute_retry_config: RetryConfig,
     pub connect_compute_locks: ApiLocks<Host>,