Summary:
88c6e7a22b / D3446871 broke the OSS version of React where React.xcodeproj isn't autogenerated.
**Test plan:** UIExplorer example works again.
Closes https://github.com/facebook/react-native/pull/8288
Differential Revision: D3466246
Pulled By: javache
fbshipit-source-id: 1240b755b0df54ddfde016d0122640293e50caeb