Remove unused-variable in dumbo/backup/dumbo/service/tests/ChainReplicatorTests.cpp +3 (facebookresearch#4024)

Summary:
Pull Request resolved: facebookresearch#4024

LLVM-15 has a warning `-Wunused-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]]`.

#buildsonlynotests - Builds are sufficient

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Differential Revision: D65755277

fbshipit-source-id: 13a2ad06375fd84e5e7afd69488e7fa36b658f20

Author: r-barnes

faiss/utils/distances_simd.cpp

@@ -3759,7 +3759,7 @@ void fvec_add(size_t d, const float* a, float b, float* c) {
     size_t i;
     simd8float32 bv(b);
     for (i = 0; i + 7 < d; i += 8) {
-        simd8float32 ci, ai, bi;
+        simd8float32 ci, ai;
         ai.loadu(a + i);
         ci = ai + bv;
         ci.storeu(c + i);