Fix wrong variable in VirtualizedSectionList highlight callback cleanup

[Nedunchezhiyan-M]

Summary

Fix a bug in _setUpdateHighlightFor where the cleanup path deletes from this._updateHighlightFor (which is a method) instead of this._updateHighlightMap (the actual map storing highlight callbacks).

This means highlight callbacks were never cleaned up when cells were removed, causing a memory leak. The $FlowFixMe[prop-missing] annotation was masking what Flow correctly identified as a type error.

For reference, the parallel method _setUpdatePropsFor at line 441 correctly uses this._updatePropsMap for its cleanup path.

Changelog:

[GENERAL] [FIXED] - Fix highlight callback cleanup in VirtualizedSectionList using wrong variable name

Test Plan

1. Render a SectionList with separator highlight support
2. Scroll through the list so cells are recycled and removed
3. Verify that highlight callbacks are properly cleaned up from _updateHighlightMap
4. Previously, deleting from the method _updateHighlightFor was a no-op, so callbacks accumulated

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