[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/binary/local_proxy.rs

@@ -279,7 +279,6 @@ fn build_config(args: &LocalProxyCliArgs) -> anyhow::Result<&'static ProxyConfig
         },
         proxy_protocol_v2: config::ProxyProtocolV2::Rejected,
         handshake_timeout: Duration::from_secs(10),
-        region: "local".into(),
         wake_compute_retry_config: RetryConfig::parse(RetryConfig::WAKE_COMPUTE_DEFAULT_VALUES)?,
         connect_compute_locks,
         connect_to_compute: compute_config,