This reverts commit 258d963e406c512bb90295c700ee22e4609abcd0.
Remove the mbr/gpt choice from softraid features for now, as it cannot be
directly used without additional commits, to be pushed soon. Furthermore, it
could even lead to instance spawn misconfiguration, if the disk label
specified in instance_info cannot fit with the boot mode + partitioning layout
(example: you build softraid over gpt, then you lose the mbr gap. Thus you need
an additional bios boot partition, in BIOS boot mode, or an esp, in UEFI boot
mode, outside the raid, for grub to install itself inthere, to be able to
assemble raid and find root device correctly).
Change-Id: I3a0a704ea99a40eb3fc8e879270dfbd356951488
316dd3f952