Robot: Ensure pins are cleaned up in on_config_reload

Note that this is still quite problematic as the StepperMotor doesn't
receive the new pins in on_config_reload. Not entirely sure how to
handle this. Perhaps update the StepperMotor's pins? Perhaps create a
new StepperMotor? This could get ugly.
Endstops: Ensure pins are cleaned up in on_config_reload
Extruder: Ensure pins are cleaned up on_config_reload
TemperatureControl: Ensure Pins are cleaned up on_config_reload
PauseButton: Ensure Pins are cleaned up on_config_reload