1. hybrid(auto) on_buildplate_only option not working correctly because
parent is not set.
2. tree(auto) on_buildplate_only not working correctly because unsupported
branch isn't deleted completely. I add child to track the dangling nodes
and then delete nodes with no child.
Change-Id: I24c69a7cf400d2961b22a720a6069cf95db6c1a5
(cherry picked from commit bce77c16128d35c668b175e7135b9fe9acd71d13)
ebf26338e8