[RISCV] Remove side effects from vsetvli intrinsics.

Delete the opt intrinsics since they are now identical.

I left the side effects due to user expectations about how these
interact with things like inline assembly or function calls. Or
that they wouldn't be hoisted. I think we should look at other
ways to address thoughs.

If I could, I'd rename them these somehow to distance them from
the vsetvli instruction. In some sense they only query the VL for
a particular SEW and LMUL. They don't guarantee a vsetvli
instruction will be emitted.

Fixes https://github.com/llvm/llvm-project/issues/59359

Reviewed By: rogfer01, kito-cheng

Differential Revision: https://reviews.llvm.org/D143220