Fix bug where removing material set items weren't consistent in how they purged materials and profiles

Previously remove_profile would purge unused materials and profiles, but
remove_layer and remove_constituent wouldn't. This was as subtle
inconsitency. Now everything by default consistently retains materials
and profiles, and has options to change this default.

src/ifcopenshell-python/ifcopenshell/api/material/remove_layer.py

@@ -15,19 +15,19 @@
 #
 # You should have received a copy of the GNU Lesser General Public License
 # along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
-import ifcopenshell
+import ifcopenshell.util.element
 
 
-def remove_layer(file: ifcopenshell.file, layer: ifcopenshell.entity_instance) -> None:
+def remove_layer(
+    file: ifcopenshell.file, layer: ifcopenshell.entity_instance, should_remove_material: bool = False
+) -> None:
     """Removes a layer from a layer set
 
     Note that it is invalid to have zero items in a set, so you should leave
     at least one layer to ensure a valid IFC dataset.
 
     :param layer: The IfcMaterialLayer entity you want to remove
-    :type layer: ifcopenshell.entity_instance
-    :return: None
-    :rtype: None
+    :param should_remove_material: If true, materials with no users will be removed
 
     Example:
 
@@ -54,6 +54,7 @@ def remove_layer(file: ifcopenshell.file, layer: ifcopenshell.entity_instance) -
         # one one side such as to line a services riser.
         ifcopenshell.api.material.remove_layer(model, layer=layer3)
     """
-    settings = {"layer": layer}
-
-    file.remove(settings["layer"])
+    material = layer.Material
+    file.remove(layer)
+    if material and should_remove_material:
+        ifcopenshell.util.element.remove_deep2(file, subelement)