Arduino I/O with Linuxcnc

I hope there are no problems caused by removing that line.

Singleton means that only one component can run. Otherwise, it is generally possible to load components in multiple instances.
The singleton then has no instance number in the signal name, because it is the only one possible.

So a normal component has eg serialreceive.0.bit-14,
singleton should eg serialreceive.bit-14.