Remove unused variables. NFC (#8972)

These were preventing the latest version of llvm from building binaryen.

This was triggered by https://github.com/llvm/llvm-project/pull/203084

See
https://logs.chromium.org/logs/emscripten-releases/buildbucket/cr-buildbucket/8674381472972128657/+/u/Build_Binaryen/stdout