efi: libstub: Drop randomization of runtime memory map

Randomizing the UEFI runtime memory map requires the use of the
SetVirtualAddressMap() EFI boot service, which we prefer to avoid. So
let's drop randomization, which was already problematic in combination
with hibernation, which means that distro kernels never enabled it in
the first place.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>