Reduce code duplication

It stays unreadable though, because of JSON.

Contributes to issue CURA-3405.

resources/definitions/ultimaker_original.def.json

@@ -62,7 +62,7 @@
             "default_value": "G21 ;metric values\nG90 ;absolute positioning\nM82 ;set extruder to absolute mode\nM107 ;start with the fan off\nG28 X0 Y0 ;move X/Y to min endstops\nG28 Z0 ;move Z to min endstops\nG1 Z15.0 F9000 ;move the platform down 15mm\nG92 E0 ;zero the extruded length\nG1 F200 E6 ;extrude 6 mm of feed stock\nG92 E0 ;zero the extruded length again\nG1 F9000\n;Put printing message on LCD screen\nM117 Printing..."
         },
         "machine_end_gcode": {
-            "value": "'M104 S0 ;extruder heater off\\nM140 S0 ;heated bed heater off (if you have it)\\nG91 ;relative positioning\\nG1 E-1 F300  ;retract the filament a bit before lifting the nozzle, to release some of the pressure\\nG1 Z+0.5 E-5 X-20 Y-20 F9000 ;move Z up a bit and retract filament even more\\nG28 X0 Y0 ;move X/Y to min endstops, so the head is out of the way\\nM84 ;steppers off\\nG90 ;absolute positioning' if machine_heated_bed else 'M104 S0 ;extruder heater off\\nG91 ;relative positioning\\nG1 E-1 F300  ;retract the filament a bit before lifting the nozzle, to release some of the pressure\\nG1 Z+0.5 E-5 X-20 Y-20 F9000 ;move Z up a bit and retract filament even more\\nG28 X0 Y0 ;move X/Y to min endstops, so the head is out of the way\\nM84 ;steppers off\\nG90 ;absolute positioning'"
+            "value": "'M104 S0 ;extruder heater off' + ('\\nM140 S0 ;heated bed heater off' if machine_heated_bed else '') + '\\nG91 ;relative positioning\\nG1 E-1 F300  ;retract the filament a bit before lifting the nozzle, to release some of the pressure\\nG1 Z+0.5 E-5 X-20 Y-20 F9000 ;move Z up a bit and retract filament even more\\nG28 X0 Y0 ;move X/Y to min endstops, so the head is out of the way\\nM84 ;steppers off\\nG90 ;absolute positioning'"
         }
     }
 }