CUDA: Simplify Clang implicit host linker settings

The purpose of `CMAKE_CUDA_HOST_IMPLICIT_LINK_*` is to capture the
extra link libraries and directories that the CUDA compiler passes
when invoking the host linker.  We need this when using NVCC because
CMake drives the host linker directly rather than through NVCC.
However, this is not needed with Clang because:

* Clang does not pass any CUDA libraries automatically.
* We drive linking with the Clang compiler anyway.

Drop the detection logic for Clang because it only gives the normal C++
runtime libraries which we do not need here.