Revert "Cleanup apt cache after grub install"

This calls chroot as a non-root user, which will always fail with
EPERM.

This reverts commit ab2d1a31f2177b26aada075201712b0061a1b771.

Change-Id: Ie674fef694ad66e1ebc22083dec2a0bc34371e7b
Merge "Revert "Cleanup apt cache after grub install""