Stop falling back on yaml when loading repo file
Remove dead code
Remove fallback on yaml when parsing manifests

It has always been exported into json hence ucl compatible the fallback
here have just hidden bugs all the time and complicated tracking them
down properly
Remove yaml related code which is not used anywhere
Remove libyaml not used anymore
Make it more clear when we speak about a major OS upgrade detected
Add real ucl files :)
Import newer libucl which among other things improve the error message