Remove position type override on scroll view sticky headers (#47498)

Summary:
Pull Request resolved: #47498

I am trying to help someone with creating a sticky header on a scrollview, specifically one that floats on the side of the scrollview instead of the top Currently we can't really do that, since utilizing `position: absolute` to layout this properly will get overriden by the header styles changed in this diff

This was only added since static was the default and we needed to apply zIndex. With proper static implementation that is no longer the case, so I think it makes sense to remove this to support this use case.

Changelog: [General] [Breaking] - `position` of sticky headers on `ScrollView` will now be taken into account

Reviewed By: rozele

Differential Revision: D65626544

fbshipit-source-id: 8d650ca7654918e692435935e7c1094c412fd9f6

packages/react-native/Libraries/Components/ScrollView/ScrollViewStickyHeader.js

@@ -301,7 +301,6 @@ const ScrollViewStickyHeaderWithForwardedRef: component(
 const styles = StyleSheet.create({
   header: {
     zIndex: 10,
-    position: 'relative',
   },
   fill: {
     flex: 1,