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
    one
  * 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.