References to original assets/widgets are left behind when replacing them in UMG

1. QAGame
2. Create a NewWidgetBlueprint
3. Add a Canvas and then a AEO Cat Item
4. Create a new animation and add a reference to the AEO Cat Item
5. Save and open up reference viewer, notice that there's a reference to AEO Cat Item
6. Add AEO Lev Item to the widget and right click in Sequencer to replace the Cat Item with the Lev Item
7. Remove the AEO Cat Item from the Widget (ie. Hierarchy Tab)
8. Save and refresh reference viewer

RESULT: There's a reference to the Cat Item and the Lev Item.

EXPECTED: Just one reference to Lev Item