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

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 commented:

Just remove the handling and keep the flag, it should be fine based off of what Artem said now that we handle this by default.

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