Remove deprecated code as of Lunar

[davetcoleman]

Addresses code comments:

#warning "This header is deprecated and will go away in ROS lunar."\
         "Please use moveit/move_group_interface/move_group_interface.h"\
         "and the class MoveGroupInterface instead of MoveGroup"

[v4hn]

post-merge insight:
we did not remove this in lunar because maintainers requested it stays in until melodic.
It is perfectly justified to remove it in melodic.

[davetcoleman]

Great, that's exactly what i did!