Remove unneeded include of distance_functions.h to avoid
duplicate symbol error during linking on Darwin.
// Copyright 2020 Oath Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#include "default_nearest_neighbor_index_factory.h"
-#include "distance_functions.h"
#include "hnsw_index.h"
#include "random_level_generator.h"
#include "inv_log_level_generator.h"
