Improve naming due to codemod (facebookresearch#4065)

Summary:
Pull Request resolved: facebookresearch#4065

improve neighbors_2 naming from codemod

Reviewed By: junjieqi

Differential Revision: D66823395

fbshipit-source-id: 90af06e7f6d917581a25311944689f82f12c93e1

Author: mengdilin

faiss/impl/HNSW.cpp

@@ -493,17 +493,17 @@ void HNSW::add_links_starting_from(
 
     ::faiss::shrink_neighbor_list(ptdis, link_targets, M, keep_max_size_level0);
 
-    std::vector<storage_idx_t> neighbors_2;
-    neighbors_2.reserve(link_targets.size());
+    std::vector<storage_idx_t> neighbors_to_add;
+    neighbors_to_add.reserve(link_targets.size());
     while (!link_targets.empty()) {
         storage_idx_t other_id = link_targets.top().id;
         add_link(*this, ptdis, pt_id, other_id, level, keep_max_size_level0);
-        neighbors_2.push_back(other_id);
+        neighbors_to_add.push_back(other_id);
         link_targets.pop();
     }
 
     omp_unset_lock(&locks[pt_id]);
-    for (storage_idx_t other_id : neighbors_2) {
+    for (storage_idx_t other_id : neighbors_to_add) {
         omp_set_lock(&locks[other_id]);
         add_link(*this, ptdis, other_id, pt_id, level, keep_max_size_level0);
         omp_unset_lock(&locks[other_id]);