[caffe2] Remove last clang-for-cuda sources (#84021)
Summary: We're no longer pursuing clang-for-cuda, so remove the last use-case.
Test Plan: CI
Reviewed By: pallab-zz
Differential Revision: D38996710
Pull Request resolved: https://github.com/pytorch/pytorch/pull/84021
Approved by: https://github.com/malfet
