[llvm] [RISCV] Remove codegen for vp_fneg, vp_fma. NFC (PR #193214)

[Luke Lau via llvm-commits]

lukel97 wrote:

> LGTM, but I think #193424 will have a merge conflict

I can wait for #193424 to land first. Thanks for your patience with all these pull requests by the way

https://github.com/llvm/llvm-project/pull/193214