do not print a leading colon of :rarm

fix a useful function ``print-end-effector-parameter-conf-from-robot``, which automatically generates information about end-effectors in Robot.conf (e.g. https://github.com/start-jsk/rtmros_tutorials/blob/master/hrpsys_ros_bridge_tutorials/catkin.cmake#L203 ), in order not to print a leading ``:`` of ``:rarm``, ``:larm``, ``:rleg`` and ``:lleg``.

I heard that the colon was removed by hand before this PR.