Remove section about URCapX in development (UniversalRobots#521)

The External Control URCapX is considered maintained rather than
developed by now, so it's fair to remove that statement. The robot setup
instructions clearly cover that for PolyScope X another URCapX is
needed, so that should suffice.

Author: urfeex

doc/images/initial_setup_images/services_polyscope5.png

@@ -46,9 +46,6 @@ table below or checkout the latest tag before the breaking changes were introduc
        replacing the Dashboard Server in version 10.11.0. It covers robot state control and loading
        and playing programs.
        From version 10.12, it also supports uploading programs to the robot and downloading programs from the robot, as well as listing existing programs on the robot.
-     - Using external control on |polyscope| X requires another URCapX for making external control
-       work. This is currently in the process of being created.
-       See `Universal Robots External Control URCapX <https://github.com/UniversalRobots/Universal_Robots_ExternalControl_URCapX>`_
 
 .. |polyscope| replace:: PolyScope