Remove nested unit conversion nodes

[andydandy74]

This stuff should be included in the respective Python nodes.

• [ ] All Intersecting Elements Of Category By BoundingBox
• [x] Document.ProjectPosition
• [x] Element.Area
• [x] Element.Materials+
• [x] FamilyType.CompoundStructureLayers
• [x] FamilyType.SetCompoundLayerWidth
• [x] Room.Finishes