[clang] [clang][CodeGen] Remove "unsafe-fp-math" attribute support (PR #162779)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

@RolandF77 Are you a good person to ask about the uses of `UnsafeFPMath` in PPCISelLowering.cpp?

https://github.com/llvm/llvm-project/pull/162779