message: fix(api): move splitting: strip step postfix
  the motor controller board ignores commands that start with a space (?)
  and so it wasn't restoring the old steps/mm setting and flipping back
  the microstepping switch after moves.
diff: @@ -1483,7 +1483,7 @@ class SmoothieDriver_3_0_0:
  for ax in split_target.keys():
  self.current[ax] = cached[ax]
  - split_postfix = step_postfix
  + split_postfix = step_postfix.strip()
  split_command = GCODES['MOVE'] + split_command_string
  else:
  split_prefix = ''
  