Summary:
It does explicitly what the comment above the export implies.
That way this warning on every use of Quick Controls 1 is gone:
WARNING: Cannot find style "org.kde.desktop" - fallback: "/usr/lib64/qt5/qml/QtQuick/Controls/Styles/Desktop"

Note that I'm not 100% sure that this does not have any
ill side effects as I don't quite understand what and where
org.kde.desktop is supposed to be.

Test Plan:
Started plasmashell and plasma-discover both with and without
the change, no difference except that the warning is now gone.

Reviewers: #plasma

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D7257