Summary:Interface to `RCTBatchedBridge` was being declared in two different implementation files. This is suboptimal, since it makes it hard to mock that class in a test.
So I've merged and moved these two definitions in `RCTBridge+Private.h`, so it's still obvious it's a private class, but can be included if you really need it.
Reviewed By: javache
Differential Revision: D3126135
fb-gh-sync-id: 173e4c5c2925be387b92deb7f99952ca7bf28588
fbshipit-source-id: 173e4c5c2925be387b92deb7f99952ca7bf28588