This code was disabled in preparation for KF 5.0 to remove kio's dependency on solid.
This is ironic because later on kio_trash brought that dependency again. But anyway, this
feature was still dead code for all of KF5 life time.
The idea of going to /dev and right-click mount/unmount just seems very weird as a GUI feature.
(Ignore the comment in the CMakeLists.txt, someone misunderstood what that code was about.
No desktop files involved there, this was about block devices themselves)