[clang] [RISCV][clang] Remove unused base type in `vfncvt` (PR #101646)

[Brandon Wu via cfe-commits]

4vtomat wrote:

> Make sense to me.
> (Do we have a way to test these generated builtins?)

I think we don't since the intrinsics are generated on demand during runtime.

https://github.com/llvm/llvm-project/pull/101646