cleanTexturePlacements
This function retrieves a list of all ‘place2dTexture’ and ‘place3dTexture’ nodes
in the scene. It determines which of those placement nodes are connected
only to the ‘defaultRenderUtilityList’ -- in other words, not actually
used for texture placement -- and deletes all of these unused nodes.
All items are disposed with a single delete command; a single Undo after this function will bring everything back.