Refactor SMG HV-edges filtering

Get rid of has-value edge filter.

It was necessary when HVE set was a flat collection. Now it is not necessary, and forces ugly patterns like use of Iterables#getOnlyElement every time we expect at most one edge (should be Optional).

Note, that querying depends on how we treat value sizes, e.g. what we return when size matches a present edge partially. For now, do not change this behavior.