Move script_phases script out of ruby file.
Move script_phases script out of ruby file.

Summary: Changelog: [internal] Move script_phases script out of react_native_pods.rb so that it's easier to review/debug.

Reviewed By: cortinico

Differential Revision: D33054423

fbshipit-source-id: 460de83a38959a1e45e37f8eda7fe364026fb571

janicduplessis/react-native,facebook/react-native,javache/react-native,facebook/react-native,javache/react-native,janicduplessis/react-native,janicduplessis/react-native,javache/react-native,javache/react-native,facebook/react-native,janicduplessis/react-native,facebook/react-native,facebook/react-native,javache/react-native,janicduplessis/react-native,janicduplessis/react-native,janicduplessis/react-native,facebook/react-native,facebook/react-native,janicduplessis/react-native,facebook/react-native,facebook/react-native,javache/react-native,javache/react-native,javache/react-native,javache/react-native