Remove unused web-vitals CRA boilerplate

reportWebVitals() was called without a handler, so the guard meant
web-vitals was never imported at runtime and nothing was measured.
Leftover from Create React App; we've no plans to wire vitals into
analytics, and if we did we'd use the current onCLS/onLCP/onINP API
rather than this v1-era shim.

Author: microbit-matt-hillsdon

package-lock.json

@@ -57,7 +57,6 @@
     "vite": "^7.3.1",
     "vscode-jsonrpc": "^9.0.0",
     "vscode-languageserver-protocol": "^3.16.0",
-    "web-vitals": "^1.1.1",
     "xterm": "4.19.0",
     "xterm-addon-fit": "^0.5.0"
   },

package.json

@@ -10,7 +10,6 @@ import "./layers.css";
 import { StrictMode } from "react";
 import { createRoot } from "react-dom/client";
 import App from "./App";
-import reportWebVitals from "./reportWebVitals";
 import { registerSW } from "virtual:pwa-register";
 import { flags } from "./flags";
 import { baseUrl } from "./base";
@@ -70,8 +69,3 @@ root.render(
     <App />
   </StrictMode>
 );
-
-// If you want to start measuring performance in your app, pass a function
-// to log results (for example: reportWebVitals(console.log))
-// or send to an analytics endpoint. Learn more: https://bit.ly/CRA-vitals
-reportWebVitals();