This reverts commit 4aee7d77.
Installing multiple kernels currently has a few drawbacks:
* liveusb-creator crashes in various creative ways on all kernels but the 486
* building VirtualBox guest modules for multiple kernels is buggy
* we did not confirm by actual testing the amd64 kernel actually helps the
sdmem process to wipe more than 3GB of RAM
So we postpone this to post-0.11.