Remove unused planner config params.

- The defaults for the longest_valid_segment_fraction are good enough.
  I played with custom fixed values to see if I could improve plan quality,
  but only increased computation times, and a marginal quality improvement.

- Removing the projection_evaluator makes moveit default to RRT-connect, which
  is faster and yields better plans than Kpiece .I still need to understand
  how default planners are chosen.