Native Animated - Fix timing animation delay on iOS

Summary:
Delay was broken with native animations on iOS. After checking what android does to handle delay, I noticed it does nothing at all since the delay is already handled when generating the animation frames. This removes all code that tried to handle delay on iOS since it is not needed and breaks it. Also updated an example to have delay in UI explorer.

Fixes #12388

**Test plan**
Tested that delay works in UIExplorer on iOS and Android.
Closes https://github.com/facebook/react-native/pull/12443

Differential Revision: D4582514

Pulled By: javache

fbshipit-source-id: dc53295e716c8476c71ccd578380962f056de2be

Examples/UIExplorer/js/NativeAnimationsExample.js

@@ -352,12 +352,12 @@ exports.examples = [
     },
   },
   {
-    title: 'Opacity without interpolation',
+    title: 'Opacity with delay',
     render: function() {
       return (
         <Tester
           type="timing"
-          config={{ duration: 1000 }}>
+          config={{ duration: 1000, delay: 1000 }}>
           {anim => (
             <Animated.View
               style={[