kcm/{gamecontroller,mouse,touchpad}: Hide when not relevant

Alexander Wilmsrequested to merge
alexanderwilms/plasma-desktop:hide-irrelevant-kcms into master

While testing, only the gamecontroller KCM was hidden. Is the relevant attribute only being considered when the KCM is shown in the sidebar, but not for secondary ones?

The code is based on 94231dc3

ENHANCEMENT: 513567

Edited by Nate Graham

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