Remove "hack" introduced with migration to moveit_msgs

[JenniferBuehler]

When migrating to moveit_msgs (instead of now deprecated household_objects_database_msgs and manipulation_msgs) a temproary "hack" was introduced: The pose of the object to be grasped is simply passed in the first pose of the primitives of CollisionObject.msg (all other primitives, meshes, etc are left empty).
This should in future be handled via /tf instead: the frame of the CollisionObject has the pose.
A thorough cleanup is required before completing #32.

This relates to issue #32 .