Revert "chore: externalize undici for bundling" (#65727)

## Why?

`undici` should be able to compile and bundle now.

- x-ref: https://github.com/vercel/next.js/pull/65243

---------

Co-authored-by: Jiachi Liu <inbox@huozhi.im>

docs/02-app/02-api-reference/05-next-config-js/serverExternalPackages.mdx

@@ -71,7 +71,6 @@ Next.js includes a [short list of popular packages](https://github.com/vercel/ne
 - `ts-node`
 - `typescript`
 - `vscode-oniguruma`
-- `undici`
 - `webpack`
 - `websocket`
 - `zeromq`

docs/03-pages/02-api-reference/03-next-config-js/serverExternalPackages.mdx

@@ -71,7 +71,6 @@ Next.js includes a [short list of popular packages](https://github.com/vercel/ne
 - `ts-node`
 - `typescript`
 - `vscode-oniguruma`
-- `undici`
 - `webpack`
 - `websocket`
 - `zeromq`

packages/next/src/lib/server-external-packages.json

@@ -51,7 +51,6 @@
   "tailwindcss",
   "ts-node",
   "typescript",
-  "undici",
   "vscode-oniguruma",
   "webpack",
   "websocket",