IfcGeom::Kernel::get_layers: remove what would appear to be unnecessary code (yields 0 layers in my tests).

The LayerAssignments() calls can take up to 95 % of the function's execution time yielding no results.

src/ifcgeom/IfcGeomFunctions.cpp

@@ -1807,20 +1807,6 @@ std::map<std::string, IfcSchema::IfcPresentationLayerAssignment*> IfcGeom::Kerne
                 layers[(*jt)->Name()] = *jt;
             }
         }
-
-        IfcRepresentationItem::list::ptr items = r->as<IfcRepresentationItem>();
-        for (IfcRepresentationItem::list::it it = items->begin(); it != items->end(); ++it) {
-            IfcPresentationLayerAssignment::list::ptr a = (*it)->
-                // LayerAssignments renamed from plural to singular, LayerAssignment, so work around that
-#ifdef USE_IFC4
-                LayerAssignment();
-#else
-                LayerAssignments();
-#endif
-            for (IfcPresentationLayerAssignment::list::it jt = a->begin(); jt != a->end(); ++jt) {
-                layers[(*jt)->Name()] = *jt;
-            }
-        }
     }
     return layers;
 }