[clang] [CUDA] Remove sema check of function declaration with variadic argument (PR #161350)

[Matt Arsenault via cfe-commits]

arsenm wrote:

I'd expect the -f flag behavior to be independent of what the backend supports. What does nvcc do? I'd expect it to require an opt-in or language standard flag 

https://github.com/llvm/llvm-project/pull/161350