[CUDA] Stop adding CUDA features twice

[CUDA] Stop adding CUDA features twice

We currently call the `addNVPTXFeatures` function in two places, inside
of the CUDA Toolchain and inside of Clang in the standard entry point.
We normally add features to the job in Clang, so the call inside of the
CUDA toolchain is redundant and results in `+ptx` features being added.
Since we remove this call, we no longer will have a cached CUDA
installation so we will usually create it twice.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D128752