Use xcodebuild and delete "Framework Search Paths" for Xcode 7.3 to un-stall the tests

Summary:The Obj-C tests were stalling when we updated TravisCI to use the OS X image with Xcode 7.3 and iOS 9.3.

On my own MBP with Xcode 7.3 the tests stall as well. Running `./scripts/objc-test.sh` prints out a warning near the end, which says `ld` couldn't find a Frameworks folder under the iPhoneSimulator9.3 SDK directory. Indeed, this directory doesn't exist on my computer. When creating a brand new project with unit tests and UI tests, both test targets don't specify "Framework Search Paths" so I don't think we need to specify it anymore.
Closes https://github.com/facebook/react-native/pull/7168

Differential Revision: D3216524

fb-gh-sync-id: 3097bda98d78289ecdba86801bcd461f3311ac47
fbshipit-source-id: 3097bda98d78289ecdba86801bcd461f3311ac47