Set default layer height via preferred quality type

So the layer heights are correct for each quality type but the default is still 0.2mm.

Contributes to issue CURA-4981.

resources/definitions/ubuild-3d_mr_bot_280.def.json

@@ -11,7 +11,8 @@
         "file_formats": "text/x-gcode",
         "icon": "icon_uBuild-3D",
         "platform": "mr_bot_280_platform.stl",
-        "has_materials": true
+        "has_materials": true,
+        "preferred_quality_type": "draft"
     },
 
     "overrides": {
@@ -24,7 +25,6 @@
         "material_diameter": { "default_value": 1.75 },
         "material_bed_temperature": { "default_value": 70 },
         "machine_nozzle_size": { "default_value": 0.4 },
-        "layer_height": { "default_value": 0.2 },
         "layer_height_0": { "default_value": 0.1 },
         "retraction_amount": { "default_value": 2 },
         "retraction_speed": { "default_value": 50 },