drop internal os-release class in favor of KOSRelease of kcoreaddons 5.58
Summary:
KOSRelease was based on our class so it is fully API compatible and doesn't
require any changes besides different include and name
Test Plan: builds + modules still loads os release data
Reviewers: davidedmundson
Reviewed By: davidedmundson
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D21209