GetClassDefaults node retains 'hidden' references to original default.

Need to add calls to Super::PinConnectionListChanged() and Super::PinDefaultValueChanged() in K2Node_GetClassDefaults.cpp.

1. Launch QAGame editor.
2. Create a new Blueprint class (BP_1). Save.
3. Create a new Blueprint class (BP_2) and open it in the BP editor.
4. Add a GetClassDefaults node.
5. Set the class input pin to "BP_1" and save.
6. Right-click on BP_1 in the Content Browser and choose "Reference Viewer..."
7. Note that BP_2 is shown as a referencer. Close the Reference Viewer window and return to editing BP_2.
8. Add a "Get reference to self" node and drag off a "GetClass" node from it.
9. Connect the output of the GetClass node to the input of the GetClassDefaults node, then save.
10. Right-click on BP_1 in the Content Browser and choose "Reference Viewer..."
11. Note that BP_2 is still shown as a referencer.
12. Close UE4 editor and restart.
13. Right-click on BP_1 in the Content Browser and choose "Reference Viewer..."
14. Note that BP_2 is still shown as a referencer.
    Expected result: BP_2 is no longer holding a reference to BP_1 after connecting the class input pin.