Realized that if you do not specify a search tree for the
EuclideanClusterExtraction, then it automatically determines if the pointcloud
is organized, and if so, it defines an organized neighbor search tree.  So
getting rid of my specification should speed up the cluster extraction a bit.
Tested this with Andy, and verified that it is faster.

NOTE: Small change to the limits for the passthrough filters.
Removed the references to the KdTree search tree.