Revert isNode workerd detection that caused Cloudflare build regression (#16997)

Author: matthewp

.changeset/spicy-pandas-retire.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Reverts a change to `isNode` runtime detection that caused a significant build time regression for Cloudflare adapter users with large prerendered sites

packages/astro/src/runtime/server/render/util.ts

@@ -275,9 +275,7 @@ export interface RendererFlusher {
 }
 
 export const isNode =
-	typeof process !== 'undefined' &&
-	Object.prototype.toString.call(process) === '[object process]' &&
-	!(typeof navigator !== 'undefined' && navigator.userAgent === 'Cloudflare-Workers');
+	typeof process !== 'undefined' && Object.prototype.toString.call(process) === '[object process]';
 // @ts-expect-error: Deno is not part of the types.
 export const isDeno = typeof Deno !== 'undefined';