Remove unused variables in faiss/tests/test_threaded_index.cpp

Summary:
LLVM-15 has a warning `-Wunused-but-set-variable` which we treat as an error because it's so often diagnostic of a code issue. Unused variables can compromise readability or, worse, performance.

This diff either (a) removes an unused variable and, possibly, it's associated code, or (b) qualifies the variable with `[[maybe_unused]]`, mostly in cases where the variable _is_ used, but, eg, in an `assert` statement that isn't present in production code.

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Reviewed By: palmje

Differential Revision: D53779512

fbshipit-source-id: 038967a05306d921cc09f48ae71b4e6d4eda6664

tests/test_threaded_index.cpp

@@ -169,7 +169,7 @@ TEST(ThreadedIndex, TestReplica) {
     int k = 6;
 
     // Try with threading and without
-    for (bool threaded : {true, false}) {
+    for ([[maybe_unused]] const bool threaded : {true, false}) {
         std::vector<std::unique_ptr<MockIndex>> idxs;
         faiss::IndexReplicas replica(d);
 
@@ -247,8 +247,6 @@ TEST(ThreadedIndex, TestShards) {
         shards.search(n, x.data(), k, distances.data(), labels.data());
 
         for (int i = 0; i < idxs.size(); ++i) {
-            auto perShard = n / idxs.size();
-
             EXPECT_EQ(idxs[i]->nCalled, n);
             EXPECT_EQ(idxs[i]->xCalled, x.data());
             EXPECT_EQ(idxs[i]->kCalled, k);