[chore][GraphQL/Limits] Clean up headers

## Description

Two header related clean-ups:

- The version header should no longer be part of the CORS
  configuration, because we don't expect versions to be configured
  by (request) header.
- The `ShowUsage` type doesn't need to implement `Header` because we
  only care about comparing its name.

## Test plan

CI

crates/sui-graphql-rpc/src/extensions/query_limits_checker.rs

@@ -12,9 +12,7 @@ use async_graphql::parser::types::{
 };
 use async_graphql::{value, Name, Pos, Positioned, Response, ServerResult, Value, Variables};
 use async_graphql_value::Value as GqlValue;
-use axum::headers;
 use axum::http::HeaderName;
-use axum::http::HeaderValue;
 use once_cell::sync::Lazy;
 use std::collections::{BTreeSet, HashMap, VecDeque};
 use std::net::SocketAddr;
@@ -48,21 +46,10 @@ struct QueryLimitsCheckerExt {
 
 pub(crate) const CONNECTION_FIELDS: [&str; 2] = ["edges", "nodes"];
 
-impl headers::Header for ShowUsage {
-    fn name() -> &'static HeaderName {
+impl ShowUsage {
+    pub(crate) fn name() -> &'static HeaderName {
         &LIMITS_HEADER
     }
-
-    fn decode<'i, I>(_: &mut I) -> Result<Self, headers::Error>
-    where
-        I: Iterator<Item = &'i HeaderValue>,
-    {
-        Ok(ShowUsage)
-    }
-
-    fn encode<E: Extend<HeaderValue>>(&self, _: &mut E) {
-        unimplemented!()
-    }
 }
 
 impl ExtensionFactory for QueryLimitsChecker {

crates/sui-graphql-rpc/src/server/builder.rs

@@ -44,7 +44,7 @@ use axum::middleware::{self};
 use axum::response::IntoResponse;
 use axum::routing::{get, post, MethodRouter, Route};
 use axum::Extension;
-use axum::{headers::Header, Router};
+use axum::Router;
 use chrono::Utc;
 use http::{HeaderValue, Method, Request};
 use hyper::server::conn::AddrIncoming as HyperAddrIncoming;
@@ -57,7 +57,7 @@ use std::net::TcpStream;
 use std::sync::Arc;
 use std::time::Duration;
 use std::{any::Any, net::SocketAddr, time::Instant};
-use sui_graphql_rpc_headers::{LIMITS_HEADER, VERSION_HEADER};
+use sui_graphql_rpc_headers::LIMITS_HEADER;
 use sui_package_resolver::{PackageStoreWithLruCache, Resolver};
 use sui_sdk::SuiClientBuilder;
 use tokio::join;
@@ -309,11 +309,7 @@ impl ServerBuilder {
             .allow_methods([Method::POST])
             // Allow requests from any origin
             .allow_origin(acl)
-            .allow_headers([
-                hyper::header::CONTENT_TYPE,
-                VERSION_HEADER.clone(),
-                LIMITS_HEADER.clone(),
-            ]);
+            .allow_headers([hyper::header::CONTENT_TYPE, LIMITS_HEADER.clone()]);
         Ok(cors)
     }