Fix scroll events getting skipped on Android

Summary:
This code related to velocity would cause some scroll events to be skipped and caused some jitter for sticky headers. Not sure if there is a better fix but removing this does fix missing events and the velocity calculation still seems to be working.

**Test plan**
Tested that sticky headers now work properly on Android, tested that velocity calculation still seem to work.
Closes https://github.com/facebook/react-native/pull/15761

Differential Revision: D5760820

Pulled By: sahrens

fbshipit-source-id: 562b5f606bdc5452ca3d85efb5e0e3e7db224891

ReactAndroid/src/main/java/com/facebook/react/views/scroll/OnScrollDispatchHelper.java

@@ -27,8 +27,6 @@ public class OnScrollDispatchHelper {
 
   private long mLastScrollEventTimeMs = -(MIN_EVENT_SEPARATION_MS + 1);
 
-  private static final float THRESHOLD = 0.1f; // Threshold for end fling
-
   /**
    * Call from a ScrollView in onScrollChanged, returns true if this onScrollChanged is legit (not a
    * duplicate) and should be dispatched.
@@ -40,11 +38,6 @@ public class OnScrollDispatchHelper {
             mPrevX != x ||
             mPrevY != y;
 
-    // Skip the first calculation in each scroll
-    if (Math.abs(mXFlingVelocity) < THRESHOLD && Math.abs(mYFlingVelocity) < THRESHOLD) {
-      shouldDispatch = false;
-    }
-
     if (eventTime - mLastScrollEventTimeMs != 0) {
       mXFlingVelocity = (float) (x - mPrevX) / (eventTime - mLastScrollEventTimeMs);
       mYFlingVelocity = (float) (y - mPrevY) / (eventTime - mLastScrollEventTimeMs);