fix(cli): ENOENT during asset publishing (aws#25869)

There was still a TOCTOU error in the file asset publishing, which could lead to `ENOENT: no such file or directory` when assets were being published in parallel.

The whole `if (fileExists) { delete; }` logic was actually not necessary, as `fs.rename` will atomically overwrite existing files already, so we can just call it directly.

Closes aws#25293.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/cdk-assets/lib/private/archive.ts

@@ -58,17 +58,18 @@ function writeZipFile(directory: string, outputFile: string): Promise<void> {
 }
 
 /**
- * Rename the file to the target location, taking into account that we may see EPERM on Windows
- * while an Antivirus scanner still has the file open, so retry a couple of times.
+ * Rename the file to the target location, taking into account:
+ *
+ * - That we may see EPERM on Windows while an Antivirus scanner still has the
+ *   file open, so retry a couple of times.
+ * - This same function may be called in parallel and be interrupted at any point.
  */
 async function moveIntoPlace(source: string, target: string, logger: Logger) {
   let delay = 100;
   let attempts = 5;
   while (true) {
     try {
-      if (await pathExists(target)) {
-        await fs.unlink(target);
-      }
+      // 'rename' is guaranteed to overwrite an existing target, as long as it is a file (not a directory)
       await fs.rename(source, target);
       return;
     } catch (e: any) {
@@ -86,18 +87,6 @@ function sleep(ms: number) {
   return new Promise(ok => setTimeout(ok, ms));
 }
 
-async function pathExists(x: string) {
-  try {
-    await fs.stat(x);
-    return true;
-  } catch (e: any) {
-    if (e.code === 'ENOENT') {
-      return false;
-    }
-    throw e;
-  }
-}
-
 function randomString() {
   return Math.random().toString(36).replace(/[^a-z0-9]+/g, '');
 }