Remove comment syntax from ReactNativeTypes (#31457)

# Summary

I'm working to get the main `react-native` package parsable by modern
Flow tooling (both `flow-bundler`, `flow-api-translator`).

This diff trivially removes some redundant Flow comment syntax in
`ReactNativeTypes.js`, which fixes parsing under these newer tools.

## How did you test this change?

Files were pasted into `react-native-github` under fbsource, where Flow
validates ✅.