libweston-desktop: Disable xdg_shell_v6
xdg_shell stable has been available for a long time, so xdg_shell_v6 should no longer be needed. However, to play it safe, we just disable it for now. We can then remove the implementation entirely later.
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xdg_shell stable has been available for a long time, so xdg_shell_v6 should no longer be needed. However, to play it safe, we just disable it for now. We can then remove the implementation entirely later.