Flow: run codemod to remove existential type

The existential type `*` was deprecated and a codemod provided to replace it. Ran that and did some manual fixups:

```sh
node_modules/.bin/flow codemod replace-existentials --write .
```

ghstack-source-id: 4c98b8db6a80159aa6ba3f2fc3659c11939da134
Pull Request resolved: https://github.com/facebook/react/pull/25416