Enable automatic step size calculation

Results seem to suggest that 1 point every 2.5 mm gives optimal results.
So, enable it.

Change-Id: I37826f9dc3cebf0480a677631e45129e12437ca6
diff --git a/frc971/control_loops/drivetrain/trajectory.h b/frc971/control_loops/drivetrain/trajectory.h
index 049dd33..1fb9062 100644
--- a/frc971/control_loops/drivetrain/trajectory.h
+++ b/frc971/control_loops/drivetrain/trajectory.h
@@ -41,8 +41,8 @@
 class Trajectory {
  public:
   Trajectory(const DistanceSpline *spline,
-             const DrivetrainConfig<double> &config,
-             double vmax = 10.0, int num_distance = 500);
+             const DrivetrainConfig<double> &config, double vmax = 10.0,
+             int num_distance = 0);
   // Sets the plan longitudal acceleration limit
   void set_longitudal_acceleration(double longitudal_acceleration) {
     longitudal_acceleration_ = longitudal_acceleration;