Fix typo in VirtualizedSectionList._setUpdateHighlightFor deleting from method instead of map

The else branch of _setUpdateHighlightFor was calling:
  delete this._updateHighlightFor[cellKey]
which targeted the arrow-function method itself rather than the
_updateHighlightMap backing store. This meant item highlight
callbacks were never cleaned up on unmount, causing a memory leak
and stale callbacks.

Fix: replace with delete this._updateHighlightMap[cellKey] to
match the symmetric _setUpdatePropsFor implementation. The
// \[prop-missing] suppression comment is also removed
since the correct target no longer triggers a Flow error.

Author: divya1234-ctrl

packages/virtualized-lists/Lists/VirtualizedSectionList.js

@@ -431,8 +431,7 @@ class VirtualizedSectionList<
     if (updateHighlightFn != null) {
       this._updateHighlightMap[cellKey] = updateHighlightFn;
     } else {
-      // $FlowFixMe[prop-missing]
-      delete this._updateHighlightFor[cellKey];
+      delete this._updateHighlightMap[cellKey];
     }
   };