This reverts commit 6a472cf4c1b78580de79c79ca7d7b714f4d8d36e. On
second thought, this is not a good idea, because it means that a
CUDA-enabled Blender doesn't work on non-CUDA systems anymore (since
they don't have libOpenCL.so in /run/opengl-driver). I guess a better
solution will be to split cudatoolkit into multiple outputs.