Remove the vbox target from the build system.

I've been told this is no longer in use, and it's the only user of
external/grub, which is distressingly out of date.

Change-Id: I434a55e0d68f6db97fa71e294e983ff1802e9ba6
(cherry picked from commit de21059acf371a58019ef02aa79457923750aa79)
10 files changed