Port from deprecated KIconLoader::IconSize()
Summary: IconSize() method is deprecated from Frameworks 5.66
Reviewers: Dolphin, elvisangelaccio, meven
Reviewed By: Dolphin, elvisangelaccio
Subscribers: kfm-devel
Tags: Dolphin
Maniphest Tasks: T11637
Differential Revision: https://phabricator.kde.org/D26237