Remove `@babel/plugin-transform-regenerator` from RN Babel preset (#789)

Summary:
## Summary

Hermes added support for generators in 0.2.0, and JSC is ES6 feature complete since r202125.

NOTE: This is a combined Metro + React Native commit. For React Native, the only change here is adding `babel/plugin-transform-regenerator` to `repo-config` ( = `devDependencies`), so the tests no longer implicitly consume it via Metro.

Changelog: [Internal]

X-link: https://github.com/facebook/metro/pull/789

Reviewed By: rh389

Differential Revision: D34819044

Pulled By: motiz88

fbshipit-source-id: fe27b2c2af0281d5309d4c16f95762d4d4935eba

repo-config/package.json

@@ -11,6 +11,7 @@
   "dependencies": {
     "@babel/core": "^7.14.0",
     "@babel/generator": "^7.14.0",
+    "@babel/plugin-transform-regenerator": "^7.0.0",
     "@react-native-community/eslint-plugin": "*",
     "@react-native/eslint-plugin-specs": ">0.0.2",
     "@reactions/component": "^2.0.2",