Summary:
This PR reduces the number of warnings in React from 68 to 18. Mostly by marking unused variables. RNTester's warnings are more than halved.
[iOS] [Fixed] - Xcode warnings
Pull Request resolved: https://github.com/facebook/react-native/pull/23553
Differential Revision: D14151339
Pulled By: hramos
fbshipit-source-id: 8255330bf910a69a4c03051d91d7b0de3fadf2d1