Update prefetch settings (#1434)

There is no reason to use prefech when we don't use any html files
caching.

Author: nikoshell

astro.config.mjs

@@ -198,7 +198,6 @@ export default defineConfig({
     domains: ["programme.europython.eu", "placehold.co"],
   },
   prefetch: {
-    prefetchAll: true,
-    defaultStrategy: "load",
+    prefetchAll: false,
   },
 });