Simplified number of solve() entry points in moveit_planners_ompl

There are too many entry points in the moveit_planners_ompl pipeline, and anyone who has worked with it knows it is overly complex. This is a small start at cleaning up the API by reducing the number of solve() functions that exist within the pipeline. The two I removed are never used except by a node called ``ompl_planner`` that no one afaik uses. I believe this node is a relic from arm_nav, etc., before move_group replaced is functionality with a service request. 

On that note, we could probably also just remove the ``ompl_planner`` because there is just too much code in this what should be simple interface.

Note: the proper way to call ``solve`` is through a planning context. 

p.s. I think I'm writing these pull requests to myself. Is anyone out there? :-)