fix output: "standalone" returning 500 error on certain pages when …

…built without pages/ (vercel#43336)

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## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
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- [ ] Related issues linked using `fixes #number`
- [ ]
[e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs)
tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

This reverts a part of the changes made in [PR
43268](vercel#43268), which is checking
whether pagesDir exists in the root/src dir before copying the output in
.next/server to .next/standalone/.next/server as this causes certain
pages to cause the script to log `Error: Cannot find module
'.next/server/pages/_document.js'` and return a `Internal Server Error`
page since Next today still depends on pages/ dir for 404 and 500 pages
and as such needs that dir in .next/standalone/.next/server.

packages/next/build/index.ts

@@ -2777,19 +2777,17 @@ export default async function build(
           })
           await promises.copyFile(filePath, outputPath)
         }
-        if (pagesDir) {
-          await recursiveCopy(
-            path.join(distDir, SERVER_DIRECTORY, 'pages'),
-            path.join(
-              distDir,
-              'standalone',
-              path.relative(outputFileTracingRoot, distDir),
-              SERVER_DIRECTORY,
-              'pages'
-            ),
-            { overwrite: true }
-          )
-        }
+        await recursiveCopy(
+          path.join(distDir, SERVER_DIRECTORY, 'pages'),
+          path.join(
+            distDir,
+            'standalone',
+            path.relative(outputFileTracingRoot, distDir),
+            SERVER_DIRECTORY,
+            'pages'
+          ),
+          { overwrite: true }
+        )
         if (appDir) {
           await recursiveCopy(
             path.join(distDir, SERVER_DIRECTORY, 'app'),