add is_system to analog sensor so internal sensors cannot be removed

interface/src/app/main/SensorsAnalogDialog.tsx

@@ -447,6 +447,7 @@ const SensorsAnalogDialog = ({
           <Box flexGrow={1} sx={{ '& button': { mt: 0 } }}>
             <Button
               startIcon={<RemoveIcon />}
+              disabled={editItem.s}
               variant="outlined"
               color="warning"
               onClick={remove}