Remove ns from robot_description parameter

[christophfroehlich]

I don't think that the namespace kinematics set here
https://github.com/ros-controls/ros2_controllers/blob/f519170c776649de11431addbfe5bba84ac3603d/admittance_controller/include/admittance_controller/admittance_rule_impl.hpp#L62-L63
should apply to the robot_description parameter, which was introduced with #83.

ns should only apply to the latter parameters, which are defined in the admittance_controller
https://github.com/ros-controls/ros2_controllers/blob/master/admittance_controller/src/admittance_controller_parameters.yaml#L34-L55

Removing fixes ros-controls/ros2_controllers#1354 and does not break the rolling version.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 80.20%. Comparing base (a0f5944) to head (3b4b9c8).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...ics_interface_kdl/src/kinematics_interface_kdl.cpp	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #91   +/-   ##
=======================================
  Coverage   80.20%   80.20%           
=======================================
  Files           4        4           
  Lines         197      197           
  Branches       35       35           
=======================================
  Hits          158      158           
  Misses         28       28           
  Partials       11       11           

Flag	Coverage Δ
unittests	80.20% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ics_interface_kdl/src/kinematics_interface_kdl.cpp	67.00% <0.00%> (ø)

[bmagyar]

I was working on fixing this on the controller side but this is much better :D thank you