Remove sns_ik_lib dependency on std_msgs

[IanTheEngineer]

I was surprised to find that I added std_msgs as a dependency of sns_ik_lib. That seems wholly unnecessary, as evidenced by a quick search:
https://github.com/RethinkRobotics-opensource/sns_ik/search?utf8=%E2%9C%93&q=std_msgs

This dependency should be removed in the future.

[rethink-forrest]

Once we remove ROS logging, we can probably also remove roscpp as a dependency.

[IanTheEngineer]

Once we remove ROS logging, we can probably also remove roscpp as a dependency.

mmmmm nope. Not if we want to ever talk to the param server.

[rethink-forrest]

Ah, we do use NodeHandle in sns_ik.cpp to parse the urdf.