Make manufacturer for base fdm- definitions unknown

They are always overwritten, but if it isn't overwritten we don't know the manufacturer for the printer.

Contributes to issue CURA-4159.

resources/definitions/fdmextruder.def.json

@@ -6,7 +6,7 @@
     {
         "type": "extruder",
         "author": "Ultimaker",
-        "manufacturer": "Ultimaker B.V.",
+        "manufacturer": "Unknown",
         "setting_version": 1,
         "visible": false
     },

resources/definitions/fdmprinter.def.json

@@ -5,9 +5,9 @@
     "metadata":
     {
         "type": "machine",
-        "author": "Ultimaker B.V.",
+        "author": "Ultimaker",
         "category": "Ultimaker",
-        "manufacturer": "Ultimaker B.V.",
+        "manufacturer": "Unknown",
         "setting_version": 1,
         "file_formats": "text/x-gcode;application/x-stl-ascii;application/x-stl-binary;application/x-wavefront-obj;application/x3g",
         "visible": false,