vboot: merge vb2_struct.h into 2struct.h

Also remove unused preamble structs in vboot_struct.h.

BUG=b:124141368, chromium:968464
TEST=make clean && make runtests
BRANCH=none

Change-Id: I8b41f24b55eba91b1f952415eda1b532732848eb
Signed-off-by: Joel Kitching <kitching@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1844601
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
16 files changed