Remove the onChange event for Slider

Summary:
The onChange event for slider isn't necessary. Instead, it uses onValueChanged.

## What motivated this change?
After D33933403, the SliderNativeComponent starts generating an onChange: true entry in its static ViewConfig's validAttributes map.

**The Problem:** Slider inherits the onChange event from RCTViewManager. And in RCTViewManager, onChange is defined as an event that doesn't generate a ViewConfig validAttribute:
1. onChange is exported from [RCTViewManager customBubblingEventTypes](https://www.internalfb.com/code/fbsource/[210a214c9da7a847dd8840cae9f8341ed39a2ff6]/xplat/js/react-native-github/React/Views/RCTViewManager.m?lines=99%2C105%2C118)
2. Events exported from customBubblingEventTypes [don't insert into validAttributes](https://www.internalfb.com/code/fbsource/[8237815744b8cf7e38d9cf107a55c015f7b1545b]/xplat/js/react-native-github/React/Views/RCTComponentData.m?lines=393-398).

To summarize:
- onChange isn't used by slider
- onChange generates an onChange: true entry in SVCs
- onChange **doesn't** generate an onChange: true entry in NVC

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D34052662

fbshipit-source-id: 76bfd75c1ecbaa40d33e2b097b1f4458bf200ac2

Libraries/Components/Slider/Slider.js

@@ -228,7 +228,6 @@ const Slider = (
       }
     : null;
 
-  const onChangeEvent = onValueChangeEvent;
   const onSlidingCompleteEvent = onSlidingComplete
     ? (event: Event) => {
         onSlidingComplete(event.nativeEvent.value);
@@ -250,7 +249,6 @@ const Slider = (
       disabled={disabled}
       maximumValue={maximumValue}
       minimumValue={minimumValue}
-      onChange={onChangeEvent}
       onResponderTerminationRequest={() => false}
       onSlidingComplete={onSlidingCompleteEvent}
       onStartShouldSetResponder={() => true}

Libraries/Components/Slider/SliderNativeComponent.js

@@ -47,7 +47,6 @@ type NativeProps = $ReadOnly<{|
   value?: WithDefault<Double, 0>,
 
   // Events
-  onChange?: ?BubblingEventHandler<Event>,
   onValueChange?: ?BubblingEventHandler<Event>,
   onSlidingComplete?: ?DirectEventHandler<Event>,
 |}>;

Libraries/Components/__tests__/__snapshots__/Slider-test.js.snap

@@ -6,7 +6,6 @@ exports[`<Slider /> should render as expected 1`] = `
   enabled={true}
   maximumValue={1}
   minimumValue={0}
-  onChange={null}
   onResponderTerminationRequest={[Function]}
   onSlidingComplete={null}
   onStartShouldSetResponder={[Function]}
@@ -27,7 +26,6 @@ exports[`<Slider /> should set disabled as false 1`] = `
   enabled={true}
   maximumValue={1}
   minimumValue={0}
-  onChange={null}
   onResponderTerminationRequest={[Function]}
   onSlidingComplete={null}
   onStartShouldSetResponder={[Function]}
@@ -53,7 +51,6 @@ exports[`<Slider /> should set disabled as false 2`] = `
   enabled={true}
   maximumValue={1}
   minimumValue={0}
-  onChange={null}
   onResponderTerminationRequest={[Function]}
   onSlidingComplete={null}
   onStartShouldSetResponder={[Function]}
@@ -79,7 +76,6 @@ exports[`<Slider /> should set disabled as true 1`] = `
   enabled={false}
   maximumValue={1}
   minimumValue={0}
-  onChange={null}
   onResponderTerminationRequest={[Function]}
   onSlidingComplete={null}
   onStartShouldSetResponder={[Function]}
@@ -105,7 +101,6 @@ exports[`<Slider /> should set disabled as true 2`] = `
   enabled={false}
   maximumValue={1}
   minimumValue={0}
-  onChange={null}
   onResponderTerminationRequest={[Function]}
   onSlidingComplete={null}
   onStartShouldSetResponder={[Function]}