build: remove leftovers from previous x86 commits

build: remove leftovers from previous x86 commits

VBoxManage is not used and the image is created with proper permisions:
0f5d0f6  image: use internal qemu-img for vmdk and vdi images drop host
         dependencies on qemu-utils and VirtualBox

Unreachable config symbols:
9e0759e  x86: merge all geode based subtargets into one

No need to define those symbols since x86_64 is subtarget of x86:
196fb76  x86: make x86_64 a subtarget instead of a standalone target

Unreachable config symbols, so remove GRUB_ROOT:
371b382  x86: remove the xen_domu subtarget

Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>