[llvm] [WebAssembly][NFC] Remove unused createWebAssemblyVecReduce (PR #210438)

[Folkert de Vries via llvm-commits]

folkertdev wrote:

Changing to `main` adds commits. Given that this is a one-liner, maybe just rebase or cherry pick or something and force push to get the state to be correct?

https://github.com/llvm/llvm-project/pull/210438