Remove deprecated controller specializations (ros-controls#2016)

Author: christophfroehlich

doc/controllers_index.rst

@@ -40,13 +40,10 @@ Controllers for Manipulators and Other Robots
    :titlesonly:
 
    Admittance Controller <../admittance_controller/doc/userdoc.rst>
-   Effort Controllers <../effort_controllers/doc/userdoc.rst>
    Forward Command Controller <../forward_command_controller/doc/userdoc.rst>
    Joint Trajectory Controller <../joint_trajectory_controller/doc/userdoc.rst>
    Parallel Gripper Controller <../parallel_gripper_controller/doc/userdoc.rst>
    PID Controller <../pid_controller/doc/userdoc.rst>
-   Position Controllers <../position_controllers/doc/userdoc.rst>
-   Velocity Controllers <../velocity_controllers/doc/userdoc.rst>
    Gpio Command Controller <../gpio_controllers/doc/userdoc.rst>
    Motion Primitive Controller <../motion_primitives_controllers/userdoc.rst>