chore(vboot_reference): strip out a lot of unneeded logic

we essentially only use vboot_reference for cgpt right now. Strip
everything else out.
feat(coreos-base/vboot_reference): bump to get cgpt next

bump to get the cgpt next utility
Merge pull request #81 from coreos/bump-vboot-ref-for-cgpt-next

Bump vboot ref for cgpt next