Summary:
Since Xcode 9 you can run multiple simultaneously. And since I believe React Native advocates using the latest version of Xcode, we can safely remove this constraint.
Updated the unit tests. Furthermore it can be found in the [Xcode release notes](https://developer.apple.com/library/content/documentation/DeveloperTools/Conceptual/WhatsNewXcode/xcode_9/xcode_9.html#//apple_ref/doc/uid/TP40004626-CH8-SW12) that multiple simulators are now supported.
This can be tested with the CLI by running `react-native run-ios` twice, but with a different `--simulator` flag, e.g.;
react-native run-ios --simulator "iPhone SE"
react-native run-ios --simulator "iPhone X"
[IOS] [ENHANCEMENT] [local-cli/runIOS/findMatchingSimulator.js] - Allow running multiple simulators
Closes https://github.com/facebook/react-native/pull/17284
Differential Revision: D7102790
Pulled By: hramos
fbshipit-source-id: 750e7039201e28a1feda2bec1e78144fd9deff98