remove tf_prefix from urdf_visualizer.h; legacy function call from tf1

[thvhauwe]

Currently, this package is unavailable to compile under ros noetic and thus Ubuntu 20.04 focal. Error when building using catkin build indicate problems with tf_prefix, a relic from tf deprecated since melodic.

This PR proposes to drop the tf_prefix from the urdf_visualizer.h, which calls to the robot_state_publisher.h header provided by ROS.

It can be seen by comparing these two classes that publishTransform method has changed from melodic --> noetic:

http://docs.ros.org/en/melodic/api/robot_state_publisher/html/classrobot__state__publisher_1_1RobotStatePublisher.html http://docs.ros.org/en/noetic/api/robot_state_publisher/html/classrobot__state__publisher_1_1RobotStatePublisher.html

Edit: related https://github.com/ros/robot_state_publisher/pull/139

Apparantly, the removal of tf_prefix is disputed as there is no drop-in replacement functionality in tf2. Using this proposed fix will allow to compile under noetic, but break visualization in rviz.