runner: Don't show hidden KCMs
This includes, at present, Background Services (kdm_kded), Plasma Renderer (kcm_qtquicksettings) and Web Search Keywords (kcm_webshortcuts).
These KCMs are intended to be hidden in the UI, and accessed by a command, e.g. plasma-desktop!2196 (merged):
For the odd case where one might need to disable something keep it as a hidden KCM invokable via CLI, we have precendent for this with the qtquicksettings KCM
With this commit, they are now hidden from search, too.