Remove AStarSpeed encoder driver

[Ezward]

https://github.com/autorope/donkeycar/blob/b1af0aacf488c938231912f89c4bfa5c2b11c649/donkeycar/parts/encoder.py#L63

This encoder driver is not referenced anywhere in the code. This is supposed to connect to a microcontroller, but there is no firmware link for this driver. So this is not usable by anyone except perhaps the original author.

The AStar microcontrollers can run Arduino, so they can use the ArduinoEncoder instead.

So if there is someone that knows about this part and can provide firmware and other documentation, please add a comment to this issue. Otherwise I think we should remove this part.

[Ezward]

This is mentioned in the encoder section of the docs, but there is no reference to it in the code and no sketch that can be loaded onto an astar microcontroller to make this work. These appear to be arduino compatible, so it could be used as an 'arduino' device using the arduino sketches in this branch https://github.com/autorope/donkeycar/tree/921-next-generation-odometer-parts/arduino. So given there is no support in the python code and no sketch referenced that would be compatible with this driver, we can remove it. We should also remove the references in the docs (https://github.com/autorope/donkeydocs/blob/master/docs/parts/odometry.md). We can still mention it as an arduino compatible microcontroller that can use those arduino sketches.