Only loop once on "cached_properties" when building slotted classes

Previously the cached_properties dict was read three times.

src/attr/_make.py

@@ -931,19 +931,13 @@ def _create_slots_class(self):
  # To know to update them.
  additional_closure_functions_to_update = []
  if cached_properties:
- # Add cached properties to names for slotting.
- names += tuple(cached_properties.keys())
-
- for name in cached_properties:
- # Clear out function from class to avoid clashing.
- del cd[name]
-
- additional_closure_functions_to_update.extend(
- cached_properties.values()
- )
-
  class_annotations = _get_annotations(self._cls)
  for name, func in cached_properties.items():
+ # Add cached properties to names for slotting.
+ names += (name,)
+ # Clear out function from class to avoid clashing.
+ del cd[name]
+ additional_closure_functions_to_update.append(func)
  annotation = inspect.signature(func).return_annotation
  if annotation is not inspect.Parameter.empty:
  class_annotations[name] = annotation