Unify doc-strings (remove type/rtype)

As this information is already provided in type hints and we don't need to maintain it in two places.

src/ifcopenshell-python/ifcopenshell/api/nest/assign_object.py

@@ -79,13 +79,10 @@ def assign_object(
 
     :param related_objects: The list of children of the nesting relationship,
         typically IfcElements.
-    :type related_objects: list[ifcopenshell.entity_instance]
     :param relating_object: The host parent of the nesting relationship,
         typically an IfcElement.
-    :type relating_object: ifcopenshell.entity_instance
     :return: The IfcRelNests relationship instance
         or `None` if `related_objects` was empty list.
-    :rtype: Union[ifcopenshell.entity_instance, None]
 
     Example:
 

src/ifcopenshell-python/ifcopenshell/api/nest/unassign_object.py

@@ -31,9 +31,7 @@ def unassign_object(file: ifcopenshell.file, related_objects: list[ifcopenshell.
 
     :param related_objects: The list of children of the nesting relationship,
         typically IfcElements.
-    :type related_objects: list[ifcopenshell.entity_instance]
     :return: None
-    :rtype: None
 
     Example: