lfs: convert to using exthelper to wrap functions
I'm not 100% sure that upgraderequirements() can be double annotated safely, but
it seems OK based on printing the address of the function being wrapped.
One thing I've noticed is that @eh.reposetup doesn't do the usual check to
ensure that it's a local repo. Should that be baked into @eh.reposetup()
somehow, possibly with a non-default option to skip the check? It seems like a
gaping hole if every function that gets registered needs to add this check.