Adapt more QML code to Qt 6

Drop custom icon & action properties from list items. In newer versions
of Qt not only they exist, but they are also marked as FINAL which breaks
loading process.

This is enough to make AudioTube run (with some changes on the AudioTube
side).

Co-Authored-By: ivan tkachenko <me@ratijas.tk>
Co-Authored-By: Jonah Brüchert <jbb@kaidan.im>