Fixed controlled component on iOS and remove unnecessary code

Summary:
Closes #4290

`mostRecentEventCount` was always being set after `text` on iOS, so let's be really explicit about the order here as we were doing on Android: always call `setNativeProps` providing the `mostRecentEventCount` before we call `onChange` or `onChangeText`.

I also ripped out storing `mostRecentEventCount` in the state, which isn't necessary since we're always doing it through `setNativeProps`.
Closes https://github.com/facebook/react-native/pull/4588

Reviewed By: svcscm

Differential Revision: D2754565

Pulled By: nicklockwood

fb-gh-sync-id: a1401f39b4e19248095517c2a3503cd2af59fa47

Examples/UIExplorer/TextInputExample.ios.js

@@ -125,6 +125,27 @@ class RewriteExample extends React.Component {
   }
 }
 
+class RewriteExampleInvalidCharacters extends React.Component {
+  constructor(props) {
+    super(props);
+    this.state = {text: ''};
+  }
+  render() {
+    return (
+      <View style={styles.rewriteContainer}>
+        <TextInput
+          multiline={false}
+          onChangeText={(text) => {
+            this.setState({text: text.replace(/\s/g, '')});
+          }}
+          style={styles.default}
+          value={this.state.text}
+        />
+      </View>
+    );
+  }
+}
+
 class TokenizedTextExample extends React.Component {
   constructor(props) {
     super(props);
@@ -313,6 +334,12 @@ exports.examples = [
       return <RewriteExample />;
     }
   },
+  {
+    title: "Live Re-Write (no spaces allowed)",
+    render: function() {
+      return <RewriteExampleInvalidCharacters />;
+    }
+  },
   {
     title: 'Auto-capitalize',
     render: function() {