layout: Remove redundant background refresh

layout: Remove redundant background refresh

When using the NVIDIA driver, textures tend to loose their pixels when
suspending. In the past we handled this by figuring out when the NVIDIA
driver was used, and reload the background whenever we noticed we
resumed from suspend.

This shouldn't be needed anymore after
https://gitlab.gnome.org/GNOME/mutter/merge_requests/600, as it should
handle this by listening to video-memory-purged signal. Thus remove our
special handling here.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1358