[flow] Eliminate a few React.Element type that will be synced to react-native (#30719)

## Summary

Flow will eventually remove the specific `React.Element` type. For most
of the code, it can be replaced with `React.MixedElement` or
`React.Node`.

When specific react elements are required, it needs to be replaced with
either `React$Element` which will trigger a `internal-type` lint error
that can be disabled project-wide, or use
`ExactReactElement_DEPRECATED`.

Fortunately in this case, this one can be replaced with just
`React.MixedElement`.

## How did you test this change?

`flow`