Collateral damage here includes:
- Remove the old Dashboard/Panel edge type. We have a new, more general edge type for "container X uses panel Y", and we don't need this edge type for anything else.
- Remove "attachPanels()" from Dashboard. Only rendering actually needs this, and it can just load the panels.
- Remove "attachPanelPHIDs()" from Dashboard. We can look at the panel refs to figure this out.
- Remove "attachProjects()" from Dashboard. Nothing uses this and it's not a very modern approach.
- getPanelPHIDs() just looks at the config now.
- Deleted some LayoutConfig-related code which is broken/obsolete.