Revert "See if it compiles without the demos (and gazebo classic)"

This reverts commit 2c047bd.

ros_controls.unstable-from-rolling.repos

@@ -19,6 +19,10 @@ repositories:
     type: git
     url: https://github.com/ros-controls/kinematics_interface.git
     version: master
+  ros-controls/ros2_control_demos:
+    type: git
+    url: https://github.com/ros-controls/ros2_control_demos.git
+    version: master
   ros-controls/control_toolbox:
     type: git
     url: https://github.com/ros-controls/control_toolbox.git