examples: update `with-orbit-components` README (#74011)
## What?
Remove below 2 lines from [`with-orbit-components`
README.md](https://github.com/vercel/next.js/blob/canary/examples/with-orbit-components/README.md).
```md
For this purpose we are extending `<App />` of injected `<ThemeProvider/>`, and also adding `@kiwicom/babel-plugin-orbit-components`.
This fork comes from [styled-components-example](https://github.com/vercel/next.js/tree/canary/examples/with-styled-components).
```
## Why?
At #73266, Both `<ThemeProvider/>` and
`@kiwicom/babel-plugin-orbit-components` were deleted.
In addition, [styled-components](https://styled-components.com/) isn't
used anymore.
### Adding or Updating Examples
- [x] The "examples guidelines" are followed from our contributing doc
https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md
- [x] Make sure the linting passes by running `pnpm build && pnpm lint`.
See
https://github.com/vercel/next.js/blob/canary/contributing/repository/linting.md
