Do not specify a Kotlin version in the RN rootProject (#33589)

Summary:
As we introduced KGP inside `ReactAndroid` (cc ShikaSD), we now need to specify a version for it (as users will consume that build on Android New Architecture.

Currently, the version is loaded in the RN `rootProject` which is not available on user's project. I'm cleaning this up.

## Changelog

[Internal] - Do not specify a Kotlin version in the RN rootProject

Pull Request resolved: https://github.com/facebook/react-native/pull/33589

Test Plan:
Tested on a nightly version with

```
npx react-native init RNNightly --version nightly
```

Reviewed By: mdvacca

Differential Revision: D35476777

Pulled By: cortinico

fbshipit-source-id: 5a819ef5fa9a6886d7b7b683f31d59cb05a49f29