Fix: Update README templates in create-next-app (#47037)

To make them up to date with other templates

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### What?



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### Why?

I was using `create-next-app` to create my new app using the new `app`
directory but found out that `README.md` is outdated:
It shows informations for API Routes, which removed in #45819 in favor
of route handlers.

---------

packages/create-next-app/templates/app/js/README-template.md

@@ -16,9 +16,7 @@ Open [http://localhost:3000](http://localhost:3000) with your browser to see the
 
 You can start editing the page by modifying `app/page.js`. The page auto-updates as you edit the file.
 
-[API routes](https://nextjs.org/docs/api-routes/introduction) can be accessed on [http://localhost:3000/api/hello](http://localhost:3000/api/hello). This endpoint can be edited in `pages/api/hello.js`.
-
-The `pages/api` directory is mapped to `/api/*`. Files in this directory are treated as [API routes](https://nextjs.org/docs/api-routes/introduction) instead of React pages.
+[http://localhost:3000/api/hello](http://localhost:3000/api/hello) is an endpoint that uses [Route Handlers](https://beta.nextjs.org/docs/routing/route-handlers). This endpoint can be edited in `app/api/hello/route.js`.
 
 This project uses [`next/font`](https://nextjs.org/docs/basic-features/font-optimization) to automatically optimize and load Inter, a custom Google Font.
 

packages/create-next-app/templates/app/ts/README-template.md

@@ -16,9 +16,7 @@ Open [http://localhost:3000](http://localhost:3000) with your browser to see the
 
 You can start editing the page by modifying `app/page.tsx`. The page auto-updates as you edit the file.
 
-[API routes](https://nextjs.org/docs/api-routes/introduction) can be accessed on [http://localhost:3000/api/hello](http://localhost:3000/api/hello). This endpoint can be edited in `pages/api/hello.ts`.
-
-The `pages/api` directory is mapped to `/api/*`. Files in this directory are treated as [API routes](https://nextjs.org/docs/api-routes/introduction) instead of React pages.
+[http://localhost:3000/api/hello](http://localhost:3000/api/hello) is an endpoint that uses [Route Handlers](https://beta.nextjs.org/docs/routing/route-handlers). This endpoint can be edited in `app/api/hello/route.ts`.
 
 This project uses [`next/font`](https://nextjs.org/docs/basic-features/font-optimization) to automatically optimize and load Inter, a custom Google Font.