Niagara Remove Pin Feature now deletes the variable completely from the Parameters Pane

This is a regression from 4.24.3 (CL-11590370). Removing a pin on a Niagara Module Script parameter will removed the variable as well.

This was reported and tested in 4.25 Preview 2 (CL-12055273). This was reproduced in Main 4.26 (CL-12063615).

1. Open the UE4 Editor and create a Blank project
2. .Create a Niagara Module Script
3. In the Parameters Pane create any variable
4. Drag that variable into the graph and select either MapGet or MapSet
5. Right-click the variable on MapGet or MapSet
6. Click remove pin

Results: The variable itself is deleted as well

Expected: The variable remains in the Parameters pane