Remove simple X move test
The calculation is not simple. We're going to have to investigate this more in order to verify that this is happening.
The problem with this test is that even if the jerk is not limiting anything any more, it still decides to decelerate slowly to the minimum planner speed (rather than using jerk) at the very last command of a series of commands. Since there was only one command, that one command was the last command so it slowly decelerated. This makes the computation more complex. We'll investigate it some day.