clean up :init method

need to conform on realrobot, gazebo, eus simulation, see #171 for discussion

-  do not need to add-controler, that is done in robot-interface :init
- do not disable joint-action-enable if gripper action is not found, gazebo did not provide gripper joint action for now
副作用はないですが，同じことは
https://github.com/jsk-ros-pkg/jsk_pr2eus/blob/master/pr2eus/robot-interface.l#L85
で処理されているのではないでしょうか？