Bump hermes-engine and react-native in /example

Removes [hermes-engine](https://github.com/facebook/hermes). It's no longer used after updating ancestor dependency [react-native](https://github.com/facebook/react-native). These dependencies need to be updated together.


Removes `hermes-engine`

Updates `react-native` from 0.64.2 to 0.70.4
- [Release notes](https://github.com/facebook/react-native/releases)
- [Changelog](https://github.com/facebook/react-native/blob/main/CHANGELOG.md)
- [Commits](facebook/react-native@v0.64.2...v0.70.4)

---
updated-dependencies:
- dependency-name: hermes-engine
  dependency-type: indirect
- dependency-name: react-native
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>