remove sed to comment out pr2_controllers (#410)

I'm not sure if this works, but comment out pr2_controllrs from packge.xml may not necessary for groovy

- package.xml is used for rosdep install, currently we run rosdep as
```
rosdep install -r -n --from-paths src --ignore-src --rosdistro $ROS_DISTRO -y
```
so pr2_controllers is not found on rosdep system, but it will be ignored
(https://github.com/start-jsk/rtmros_common/blob/master/.travis.yml#L54)
(`  -r                    Continue installing despite errors.`)

- when it compiles, it did not checks package.xml
- when it build dep package, they uses https://github.com/tork-a/rtmros_common-release/blob/patches/release/groovy/hrpsys_ros_bridge/0001-Commentout-a-dependency-on-pr2-catkin-package-that-d.patch, so it is commented out during build process