Clean up unused files and trees (development or 2007)

Clean up unused development files and relics of the 2007 model:

• 2007 mfd-trees in subduction/interface/Aleutian Arc/mfd-map.json (see unreferenced IDs at the bottom of the workbook attached to #19 (closed))
• Development gmm-trees: subduction/interface/gmm-tree-*.json
• Development gmm-trees: subduction/slab/gmm-tree-*.json
• Development mfd-trees: subduction/slab/mfd-map-all.json