dont remove .vercel/output directory (#5555)

* dont remove .vercel/output directory - fixes #5207

* empty out .func dir before repopulating

Author: Rich-Harris

.changeset/twenty-vans-divide.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-vercel': patch
+---
+
+Don't remove .vercel/output directory

packages/adapter-vercel/index.js

@@ -93,7 +93,6 @@ export default function ({ external = [], edge, split } = {}) {
 
 			const tmp = builder.getBuildDirectory('vercel-tmp');
 
-			builder.rimraf(dir);
 			builder.rimraf(tmp);
 
 			const files = fileURLToPath(new URL('./files', import.meta.url).href);
@@ -295,6 +294,8 @@ function get_node_version() {
  * @param {string} runtime
  */
 async function create_function_bundle(builder, entry, dir, runtime) {
+	fs.rmSync(dir, { force: true, recursive: true });
+
 	let base = entry;
 	while (base !== (base = path.dirname(base)));