Don't send JSON file to back-end any more

They are no longer using it.

The back-end now just takes all settings that come in via setting messages. It doesn't need to set its defaults any more because all settings are set at the beginning. Only when slicing via command line does it need a JSON file.

Contributes to issue CURA-4410.

plugins/CuraEngineBackend/CuraEngineBackend.py

@@ -178,8 +178,7 @@ class CuraEngineBackend(QObject, Backend):
     #   This is useful for debugging and used to actually start the engine.
     #   \return list of commands and args / parameters.
     def getEngineCommand(self) -> List[str]:
-        json_path = Resources.getPath(Resources.DefinitionContainers, "fdmprinter.def.json")
-        return [self._application.getPreferences().getValue("backend/location"), "connect", "127.0.0.1:{0}".format(self._port), "-j", json_path, ""]
+        return [self._application.getPreferences().getValue("backend/location"), "connect", "127.0.0.1:{0}".format(self._port), ""]
 
     ##  Emitted when we get a message containing print duration and material amount.
     #   This also implies the slicing has finished.