delete edge when needed + small refactoring for removing dummy edges
delete edge when needed + small refactoring for removing dummy edges

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