[Vectorize] Fix unused variable warnings (NFC)
/llvm-project/llvm/lib/Transforms/Vectorize/SandboxVectorizer/Passes/TransactionAcceptOrRevert.cpp:24:8: error: unused variable 'CostBefore' [-Werror,-Wunused-variable]
auto CostBefore = SB.getBeforeCost();
^
/llvm-project/llvm/lib/Transforms/Vectorize/SandboxVectorizer/Passes/TransactionAcceptOrRevert.cpp:25:8: error: unused variable 'CostAfter' [-Werror,-Wunused-variable]
auto CostAfter = SB.getAfterCost();
^
2 errors generated.
