⏪ Revert the LSP notes in testing.md

The protocol cross-link and the TS-internal shutdown-race explanation were
too detailed for the category doc. The helper comment keeps a short,
self-contained note on the stdin-EOF workaround.

src/util/__tests__/lsp-completion.ts

@@ -145,10 +145,9 @@ export class LspSession {
         return (
             this.#connection
                 .sendRequest(ShutdownRequest.type)
-                // The TS 7 Go server races a background task against the `exit`
-                // notification and logs a bare `context canceled` to stderr as it
-                // tears down (see development/testing.md § Autocomplete). EOF on
-                // stdin shuts it down cleanly instead: exit 0, no output.
+                // The TS 7 Go server logs a bare `context canceled` to stderr
+                // when it handles `exit`; EOF on stdin shuts it down cleanly
+                // (exit 0, no output) instead.
                 .then(() => {
                     this.#child.stdin.end();
                 })