Fix freezing ScrollView problem

## Description

Fixes #1701 

## Changes

- Reverted 95e76c5
The fix introduced with 95e76c5 is no longer valid as we override EventDispatcher. 

### Before

https://user-images.githubusercontent.com/4061838/107160873-38df4080-6999-11eb-8795-12990861c3e7.mp4

### After

https://user-images.githubusercontent.com/4061838/107160879-40064e80-6999-11eb-9d34-12d60d639691.mp4

## Test code and steps to reproduce

https://gist.github.com/gorhom/06e4c7f429ee1f6ab2d9a1c27dc9aa60

## Checklist

ios/native/NativeMethods.mm

@@ -37,14 +37,10 @@
 }
 
 
-NSString *eventDispatcherKey = @"eventDispatcher";
 void scrollTo(int scrollViewTag, RCTUIManager *uiManager, double x, double y, bool animated) {
   UIView *view = [uiManager viewForReactTag:@(scrollViewTag)];
   RCTScrollView *scrollView = (RCTScrollView *) view;
-  RCTEventDispatcher* oldEventDispatcher = [scrollView valueForKey:eventDispatcherKey];
-  [scrollView setValue:nil forKey:eventDispatcherKey];
   [scrollView scrollToOffset:(CGPoint){(CGFloat)x, (CGFloat)y} animated:animated];
-  [scrollView setValue:oldEventDispatcher forKey:eventDispatcherKey];
 }
 
 }