[inductor] Remove import check for fast_flush (#88812)
https://github.com/pytorch/pytorch/pull/88557/ has a guard to make sure that triton's `do_bench` includes the `fast_flush` argument. Since we've updated Triton to a sufficiently recent revision, we can remove that guard.
Differential Revision: [D41185280](https://our.internmc.facebook.com/intern/diff/D41185280/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88812
Approved by: https://github.com/soumith
