fix: remove shutdown_flag param to run_login_server() (#2399)

In practice, this was always passed in as `None`, so eliminated the
param and updated all the call sites.

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* __->__ #2399
* #2398
* #2396
* #2395
* #2394
* #2393
* #2389

codex-rs/cli/src/login.rs

@@ -14,7 +14,7 @@ use std::path::PathBuf;
 
 pub async fn login_with_chatgpt(codex_home: PathBuf) -> std::io::Result<()> {
     let opts = ServerOptions::new(codex_home, CLIENT_ID.to_string());
-    let server = run_login_server(opts, None)?;
+    let server = run_login_server(opts)?;
 
     eprintln!(
         "Starting local login server on http://localhost:{}.\nIf your browser did not open, navigate to this URL to authenticate:\n\n{}",