sys/proc: remove GetSystemCPUUsage as it is unused
sys/proc: remove GetSystemCPUUsage as it is unused

After e115b52ce2516ead331522c965fab93b62d4041e was merged, this
function was no longer in use, so we should be able to remove it.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

dmcgowan/containerd,thaJeztah/containerd,mikebrow/containerd,containerd/containerd,containerd/containerd,thaJeztah/containerd,dmcgowan/containerd,vdemeester/containerd,estesp/containerd,crosbymichael/containerd,mikebrow/containerd,vdemeester/containerd,estesp/containerd,crosbymichael/containerd