Update layout server and svelte files to use USING_VERCEL environment variable

src/routes/+layout.server.ts

@@ -1,21 +1,17 @@
 import type { LayoutServerLoad, PageServerLoad } from "./$types";
-import { inject } from "@vercel/analytics";
-import { injectSpeedInsights } from "@vercel/speed-insights/sveltekit";
-
-if (process.env.USING_VERCEL === "true") {
-  inject();
-  injectSpeedInsights();
-}
+import { USING_VERCEL } from "$env/static/private";
 
 export const load: LayoutServerLoad = async (event) => {
   if (event.locals.user) {
     return {
       user: event.locals.user,
       isServerSetup: event.locals.isServerSetup,
+      usingVercel: USING_VERCEL,
     };
   }
   return {
     user: null,
     isServerSetup: event.locals.isServerSetup,
+    usingVercel: USING_VERCEL,
   };
 };