Upgrade to React v15.3.0-rc.2

Summary:
There were several fixes to how calls to propType checkers. This is to
account for the new deprecation warning - React.PropTypes will not be
part of production builds in the future.

Note: There is still a warning about an invalid argument to `React.PropTypes.oneOf` (React is running that validation sooner now). Specifically [both of these](https://github.com/facebook/react-native/blob/b1e49832ef3f9ffb0e5da2da7f847a8fae1d9c35/Libraries/Components/Touchable/TouchableWithoutFeedback.js#L44-L45) because `View.AccessibilityTraits` is actually undefined in tests (didn't look into why you conditionally set that).

**Test plan (required)**

`npm test` & fixed all warnings due to proptype secret
Closes https://github.com/facebook/react-native/pull/8758

Reviewed By: zpao

Differential Revision: D3564288

Pulled By: bestander

fbshipit-source-id: 1ff1f90907f41855e364048aa730ccd239c522b4