rtt_gazebo_activity: removed find_package(Orocos-KDL REQUIRED) from CMakeLists.txt as KDL is not used in rtt_gazebo_activity

These lines have been added during the merge in https://github.com/jhu-lcsr/rtt_gazebo/commit/f3b99b76a1404b46ea66bd15f0dd02e5e7b25fba.
Merge remote-tracking branch 'meyerj/removed-orocos-kdl-from-rtt-gazebo-activity'
rtt_gazebo_plugin: updated CMakeLists.txt to use orocos_kdl instead of Orocos-KDL to find KDL
Merge pull request #14 from meyerj/orocos_kdl_renaming

Orocos kdl renaming