remove duplicated machine_heated_bed

resources/definitions/zav_base.def.json

@@ -147,7 +147,6 @@
         "machine_height":                    {"default_value": 270},
         "machine_extruder_count":            {"value": 1}, 
         "machine_buildplate_type":           {"value": "glass"},
-        "machine_heated_bed":                {"default_value": true},
         "machine_center_is_zero":            {"default_value": false},
         "machine_gcode_flavor":              {"default_value": "RepRap (Marlin/Sprinter)"},
         "machine_head_with_fans_polygon":    {"default_value": [