Reverted quotes around UIKit import

Author: chrfalch

packages/react-native/scripts/ios-prebuild/templates/React-umbrella.h

@@ -6,7 +6,7 @@
  */
 
 #ifdef __OBJC__
-#import "UIKit/UIKit.h"
+#import <UIKit/UIKit.h>
 #else
 #ifndef FOUNDATION_EXPORT
 #if defined(__cplusplus)