If you want to get rid of either the 2D or 3D component of a symbol, first change to either the Top/Plan view if deleting the 2D component or change to a 3D view if you would like to delete the 3D object. Now simply edit the symbol and choose the 2D or 3D component. Then Edit > Select All, and delete the objects. Press the exit symbol button. This will leave you with either just a 2D or 3D symbol depending on which part you deleted.
Edited by JimW