[llvm] [NFC] LLVM reduce: remove unused variable (PR #133584)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-win-fast` running on `as-builder-3` while building `llvm` at step 6 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/2/builds/20473

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (build-unified-tree) failure: build (failure)
...
[4129/4157] Linking CXX executable bin\sancov.exe
[4130/4157] Linking CXX executable bin\yaml2obj.exe
[4131/4157] Linking CXX executable bin\obj2yaml.exe
[4132/4157] Linking CXX executable bin\clang-linker-wrapper.exe
[4133/4157] Linking CXX executable bin\clang-scan-deps.exe
[4134/4157] Linking CXX executable bin\clang-diff.exe
[4135/4157] Linking CXX executable bin\clang-installapi.exe
[4136/4157] Linking CXX executable bin\clang-extdef-mapping.exe
[4137/4157] Linking CXX executable bin\clang-refactor.exe
[4138/4157] Building CXX object tools\llvm-reduce\CMakeFiles\llvm-reduce.dir\deltas\ReduceOperandsToArgs.cpp.obj
FAILED: tools/llvm-reduce/CMakeFiles/llvm-reduce.dir/deltas/ReduceOperandsToArgs.cpp.obj 
C:\ninja\ccache.exe C:\PROGRA~1\MICROS~2\2022\COMMUN~1\VC\Tools\MSVC\1438~1.331\bin\Hostx64\x64\cl.exe  /nologo /TP -DGTEST_HAS_RTTI=0 -DLLVM_BUILD_STATIC -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\llvm-reduce -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\tools\llvm-reduce -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:preprocessor /Zc:__cplusplus /Oi /bigobj /permissive- /W4 -wd4141 -wd4146 -wd4244 -wd4267 -wd4291 -wd4351 -wd4456 -wd4457 -wd4458 -wd4459 -wd4503 -wd4624 -wd4722 -wd4100 -wd4127 -wd4512 -wd4505 -wd4610 -wd4510 -wd4702 -wd4245 -wd4706 -wd4310 -wd4701 -wd4703 -wd4389 -wd4611 -wd4805 -wd4204 -wd4577 -wd4091 -wd4592 -wd4319 -wd4709 -wd5105 -wd4324 -wd4251 -wd4275 -w14062 -we4238 /Gw /O2 /Ob2 /DNDEBUG -MD  /EHs-c- /GR- -std:c++17 /showIncludes /Fotools\llvm-reduce\CMakeFiles\llvm-reduce.dir\deltas\ReduceOperandsToArgs.cpp.obj /Fdtools\llvm-reduce\CMakeFiles\llvm-reduce.dir\ /FS -c C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\tools\llvm-reduce\deltas\ReduceOperandsToArgs.cpp
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\tools\llvm-reduce\deltas\ReduceOperandsToArgs.cpp(112): error C2248: 'llvm::FPMathOperator::setFastMathFlags': cannot access private member declared in class 'llvm::FPMathOperator'
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\include\llvm/IR/Operator.h(264): note: see declaration of 'llvm::FPMathOperator::setFastMathFlags'
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\include\llvm/IR/Operator.h(205): note: see declaration of 'llvm::FPMathOperator'
[4139/4157] Linking CXX executable bin\llvm-split.exe
[4140/4157] Linking CXX executable bin\llvm-opt-fuzzer.exe
[4141/4157] Linking CXX executable bin\clang-nvlink-wrapper.exe
[4142/4157] Linking CXX shared library bin\LTO.dll
[4143/4157] Linking CXX executable bin\llvm-lto.exe
[4144/4157] Linking CXX executable bin\llvm-lto2.exe
[4145/4157] Linking CXX shared library bin\libclang.dll
[4146/4157] Linking CXX executable bin\opt.exe
[4147/4157] Linking CXX executable bin\clang-check.exe
[4148/4157] Linking CXX executable bin\clang-import-test.exe
[4149/4157] Linking CXX executable bin\clang-repl.exe
[4150/4157] Linking CXX executable bin\clang.exe
[4151/4157] Generating export list for LLVM-C
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/133584