Switch to babel-preset-react-native and remove jest-preset-expo when ejecting to plain React Native project

[brentvatne]

Related to:

• Remove jest-preset-expo on eject #47
• npm test always fails #199

When you eject to a plain React Native project, we install "babel-preset-react-native" and change the preset used in .babelrc to "react-native".

[fson]

The template .babelrc file uses babel-preset-expo, which extends babel-preset-react-native by adding decorator support. I think this makes it possible to use decorators in CRNA apps. If we replace the "expo" preset with "react-native", wouldn't it break any app that relies on the decorator support?

[brentvatne]

@fson - good point, we should use babel-preset-react-native-stage-0/decorator-support (this is the same preset that babel-preset-expo extends)

[fson]

This was added in #328.