Revert "Add unprivilleged container."

The rootfs image is downloaded from http://images.linuxcontainers.org/
when using unprivilleged container.
I cannot be used this image according to my policy,
because it is not the image that distributor is officially distributed.

This reverts commit 8ac93da13e845c20e2d0e7f115e929ca1f240850.