Only enable extruder switch retraction settings if multi-extrusion

Otherwise there can't be any extruder switches.

resources/definitions/fdmprinter.def.json

@@ -5773,7 +5773,7 @@
                     "description": "The amount of retraction when switching extruders. Set to 0 for no retraction at all. This should generally be the same as the length of the heat zone.",
                     "type": "float",
                     "unit": "mm",
-                    "enabled": "retraction_enable",
+                    "enabled": "retraction_enable and extruders_enabled_count > 1",
                     "default_value": 20,
                     "value": "machine_heat_zone_length",
                     "minimum_value_warning": "0",
@@ -5787,7 +5787,7 @@
                     "description": "The speed at which the filament is retracted. A higher retraction speed works better, but a very high retraction speed can lead to filament grinding.",
                     "type": "float",
                     "unit": "mm/s",
-                    "enabled": "retraction_enable",
+                    "enabled": "retraction_enable and extruders_enabled_count > 1",
                     "default_value": 20,
                     "minimum_value": "0.1",
                     "minimum_value_warning": "1",
@@ -5803,7 +5803,7 @@
                             "description": "The speed at which the filament is retracted during a nozzle switch retract.",
                             "type": "float",
                             "unit": "mm/s",
-                            "enabled": "retraction_enable",
+                            "enabled": "retraction_enable and extruders_enabled_count > 1",
                             "default_value": 20,
                             "value": "switch_extruder_retraction_speeds",
                             "minimum_value": "0.1",
@@ -5819,7 +5819,7 @@
                             "description": "The speed at which the filament is pushed back after a nozzle switch retraction.",
                             "type": "float",
                             "unit": "mm/s",
-                            "enabled": "retraction_enable",
+                            "enabled": "retraction_enable and extruders_enabled_count > 1",
                             "default_value": 20,
                             "value": "switch_extruder_retraction_speeds",
                             "minimum_value": "0.1",
@@ -5840,7 +5840,7 @@
                     "default_value": 0,
                     "minimum_value_warning": "0",
                     "maximum_value_warning": "100",
-                    "enabled": "retraction_enable",
+                    "enabled": "retraction_enable and extruders_enabled_count > 1",
                     "settable_per_mesh": false,
                     "settable_per_extruder": true
                 }