Add code to remove last - in npc_spawn.json generation.

This should make the auto-generated json have less diffs than it currently does. The remaining diffs are due to sorting differences (which probably should actually be changed)

Old

  {
    "npc_id": "2362",
    "loc_data": "{2330,3163,0,1,3}-"
  }

New

  {
    "npc_id": "2362",
    "loc_data": "{2330,3163,0,1,3}"
  }