message: Simplify reset_uids()
  Remove unnecessary dict clearance code
diff: @@ -211,10 +211,8 @@ def get_uid(prefix=''):
  def reset_uids():
  """Resets graph identifiers.
  """
  - per_graph_object_name_uids = PER_GRAPH_OBJECT_NAME_UIDS
  - keys = list(per_graph_object_name_uids.keys())
  - for key in keys:
  - del per_graph_object_name_uids[key]
  +
  + PER_GRAPH_OBJECT_NAME_UIDS.clear()
  @keras_export('keras.backend.clear_session')
  