remove view-media-playlist from preferences icons

Summary: the view-media-playlist icon in the preferences folder looks completely different than in the actions folder and shadows the action icon when using sizes > 24px, so remove it

Reviewers: Breeze, VDG, andreaska, andreask

Reviewed By: andreask

Subscribers: andreask, Frameworks

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D10293