add decluster method tree (equal 1/3 weights) for sscn grids

stable-crust/grid/sscn/gk/adaptive/rate-tree.json

stable-crust/grid/sscn/gk/adaptive/rupture-sets.json

stable-crust/grid/sscn/gk/fixed/rate-tree.json

stable-crust/grid/sscn/gk/fixed/rupture-sets.json

stable-crust/grid/sscn/gk/source-tree.json

stable-crust/grid/sscn/nn/adaptive/rate-tree.json

stable-crust/grid/sscn/nn/adaptive/rupture-sets.json

stable-crust/grid/sscn/nn/fixed/rate-tree.json

stable-crust/grid/sscn/nn/fixed/rupture-sets.json

stable-crust/grid/sscn/nn/source-tree.json

stable-crust/grid/sscn/r85/adaptive/rate-tree.json

stable-crust/grid/sscn/r85/adaptive/rupture-sets.json

stable-crust/grid/sscn/r85/fixed/rate-tree.json

stable-crust/grid/sscn/r85/fixed/rupture-sets.json

stable-crust/grid/sscn/r85/source-tree.json

stable-crust/grid/sscn/source-tree.json