fix destroy group for control nodes (remove edges)
fix destroy group for control nodes (remove edges)

rdebroiz/dtk,d-tk/dtk,d-tk/dtk,NicolasSchnitzler/dtk,d-tk/dtk,rdebroiz/dtk,d-tk/dtk,NicolasSchnitzler/dtk,NicolasSchnitzler/dtk,d-tk/dtk,NicolasSchnitzler/dtk,rdebroiz/dtk,d-tk/dtk,rdebroiz/dtk