As it turns out the reason for the workaround was a bug
in wlroots which got fixed in the meantime.
So to keep things simple just revert the workaround and
depend on the wlroots fix instead.
To update the wlroots subproject use
meson subprojects update wlroots
This reverts commit e87aa19066.
wlr_scene_buffers need an additional wlr_scene_buffer_set_source_box()
to be scaled correctly by wlroots based on the output scale.
With this commit the buffers are now scaled correctly but, especially
on higher scale factors, may be a bit blurry.
In the future we likely want a dynamic font label generator based
on the maximal scale of all the outputs the specific buffer is currently on.
Some inspiration for that could be
https://github.com/Nefsen402/sway/blob/scene-graph/sway/sway_text_buffer.cFixes#348
