Remove obsolete_kickoffrc.js

It was broken by a609b639

Eike Hein, the original author of the script said it was OK to remove this:

> Should be fine. This script was written when Kickoff (the old menu UI)
> was ported to the backend of Kicker (the newer cacasing menu).
> This happened early in the Plasma 5 series and at least one or two
> LTS branches ago. I don't think it's worth keeping alive anymore.