Revert "Merge pull request #26 from vrabaud/fix_xacro"

Breaks groovy (xacro no catkin package), but will be required from hydro on

This reverts commit 321424a634a309ea9c284cf027074cdeda2a3c67, reversing
changes made to 383d285e01997e585bfa731525ce5f17a6cc3165.