Update GPU support documentation wrt new CUDA & libraries host_injections install script

[trz42]

After EESSI/software-layer#772 we don't need the script /cvmfs/software.eessi.io/versions/2023.06/scripts/gpu_support/nvidia/install_cuda_host_injections.sh any longer. It is replaced with /cvmfs/software.eessi.io/versions/2023.06/scripts/gpu_support/nvidia/install_cuda_and_libraries.sh. Thus, it should be removed and the documentation for GPU support should be updated accordingly (using the new script).

See accompanying issue EESSI/software-layer#789 in EESSI/software-layer.