[llvm] [RISCV] Remove vmv.s.x and vmv.x.s lmul pseudo variants (PR #71501)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Thanks! I have never thought it would be so easy.

A bit of context I should probably mention, it's easy to do now because https://github.com/llvm/llvm-project/pull/69788 has landed. Prior to that removing the LMUL information from the pseudos resulted in a lot of extra vsetvli toggles

https://github.com/llvm/llvm-project/pull/71501