[llvm] [LLVM][NVPTX] Remove nonexistent ftz ops (PR #106100)

[Billy Zhu via llvm-commits]

zyx-billy wrote:

Thanks! I added a ftz flavored case to the `bf16-instructions.ll` test to cover both codegen filecheck & ptxas-verify. I only added it for sm_80 to minimize repetition (LMK if you'd prefer it for all 3 existing sm versions tho).

https://github.com/llvm/llvm-project/pull/106100