removed unnecessary nested gmm files

volcanic/grid/non-summit/shallow/gmm-config.json

-{
-  "max-distance": 300.0
-}

volcanic/grid/non-summit/shallow/gmm-tree.json

-[
-  { "id": "ATKINSON_10", "weight": 0.2 },
-  { "id": "ASK_14", "weight": 0.2 },
-  { "id": "BSSA_14", "weight": 0.2 },
-  { "id": "CB_14", "weight": 0.2 },
-  { "id": "CY_14", "weight": 0.2 }
-]

volcanic/grid/summit/shallow/gmm-config.json

-{
-  "max-distance": 300.0
-}

volcanic/grid/summit/shallow/gmm-tree.json

-[
-  { "id": "ATKINSON_10", "weight": 0.2 },
-  { "id": "ASK_14", "weight": 0.2 },
-  { "id": "BSSA_14", "weight": 0.2 },
-  { "id": "CB_14", "weight": 0.2 },
-  { "id": "CY_14", "weight": 0.2 }
-]