Fix more printer-linter warnings.

done as part of CURA-11379

resources/definitions/Mark2_for_Ultimaker2.def.json

@@ -140,7 +140,6 @@
         "prime_tower_position_y": { "value": "170" },
         "retraction_amount": { "default_value": 5.1 },
         "retraction_speed": { "default_value": 25 },
-        "speed_wall_x": { "value": "speed_wall" },
         "switch_extruder_prime_speed":
         {
             "enabled": false,

resources/definitions/dxu.def.json

@@ -134,7 +134,6 @@
         "prime_tower_position_x": { "value": "200" },
         "retraction_amount": { "default_value": 6.5 },
         "retraction_speed": { "default_value": 25 },
-        "speed_wall_x": { "value": "speed_wall" },
         "switch_extruder_prime_speed":
         {
             "enabled": false,