Summary:
Motivation: reduce build noise that might worry new users or hide real problems.
This deals with four of the warnings currently in the iOS build. The `__unused` additions are standard and self-explanatory, following the style used elsewhere in RN. I've used `#pragma unused` to deal with parameters named by macros.
Tested by building and running the `UIExplorer` example app in XCode 8.2
Closes https://github.com/facebook/react-native/pull/11797
Differential Revision: D4396611
fbshipit-source-id: 728e9ebb94d147f7a2cbc674a25fe67e66e2e8b2
2d8a287f9c