ScrollView should not use RefreshControl on tvOS

Summary:
**Motivation**: On tvOS, Flatview and other components that use ScrollView with a RefreshControl will break without this change.

**Test plan**: Manual testing on tvOS simulator.
Closes https://github.com/facebook/react-native/pull/12751

Differential Revision: D4669503

fbshipit-source-id: 320036571788dc0102ec2611492d0fc97bceb53b

Libraries/Components/ScrollView/ScrollView.js

@@ -682,9 +682,10 @@ const ScrollView = React.createClass({
     if (refreshControl) {
       if (Platform.OS === 'ios') {
         // On iOS the RefreshControl is a child of the ScrollView.
+        // tvOS lacks native support for RefreshControl, so don't include it in that case
         return (
           <ScrollViewClass {...props} ref={this._setScrollViewRef}>
-            {refreshControl}
+            {Platform.isTVOS ? null : refreshControl}
             {contentContainer}
           </ScrollViewClass>
         );