SDDM doesn't support selecting keyboard layouts on Wayland, and it's
unlikely to be fixed anytime soon without a generic Wayland or DBus
protocol.
As the functionality is missing, it's fine to remove the layout box with
its unsightly placeholder entry.
Qt6 defers the URL resolution to the component that actually uses the
property. Which means that the images are now resolved relatively to the
corresponding sddm component (Background, ComboBox) instead of a theme.
Work around that by pinning resource URLs to the theme path with
`Qt.resolvedUrl()`.
Fixes following error:
```
file:///usr/lib64/qt6/qml/SddmComponents/ComboBox.qml:105:9: QML Image: Cannot open: file:///usr/lib64/qt6/qml/SddmComponents/angle-down.png
```
The background and the screenshot are omitted, as we don't intend to use
these images.
Source: github.com/sddm/sddm@501129294be1487f753482c29949fc1c19ef340e
License: CC-BY-SA-3.0 AND MIT
